What you could do, is to send those parallel importers & retailers a legal letter (get a lawyer, they should know which letter). In the letter, mentioned that you're the sole distributor of Food Brand ABC as appointed by the brand owner/manufacturer in Indonesia (do attach your letter of appointment) & that they're liable of unauthorized sale of Food Brand ABC in Malaysia. Legal action can & will be taken for unauthorized sale or distribution after xx-xxx-xx (insert a deadline for them usually a month or so). However if they would like to continue selling, they may buy from your company instead. Then provide them the options available for them if they would like to legally sell it e.g. appointed agent, sub-distributors, authorized reseller, authorized dealer, stockist etc etc (any fancy titles you want).  

Some parallel importers don't realize there's a sole distributor already. So if things worked out well, you'll get a new customer.

Some parallel importers don't care, so prepare to deal with them legally.

But like others who already mentioned, parallel importers exist because of market forces. Strongly suggest for you to take the market forces seriously, especially the pricing. If the parallel importers can earn WITHOUT GETTING the distributor's discount from manufacturer, do relook at your product pricing cause they most likely won't be bothered with your reseller/dealer scheme. As long as there's a gap in the market forces, parallel importers will pop up eventually. If you stop 1 today, 2 will pop up tomorrow. As the saying goes; wherever there's sugar, there'll be ants. So the root of your problem, is in your 4Ps.

The main question is, who can grant you area exclusivity & how it's being enforced?

If the China manufacturer has 3 wholesaler, what's stopping the 2nd & 3rd wholesaler to compete with you in Malaysia? If the manufacturer or the brand owner themselves isn't bothered, then your "sole distributor/agent" is just a fancy title with no backings to it.

Ultimately exclusive or sole distributorship is just an agreement between you & the brand owner. Thus, it's up to the brand owner to take action cause you have no authority over the brand. I think the common legal action that can be taken is the brand owner gets a court injunction to stop the unauthorized reseller from selling their own product. But you're not dealing with the brand owner. So, unless you have their support......doubt there's anything you can do with the other resellers here.

Well if the brand owner can back you up, then you have better chance. So suit up & try to get local injunction to stop them from selling it in Malaysia.

In your case, if manufacturer wants to appoint sole distributors in every country, they wouldnt need to appoint a wholesaler or they instruct wholesaler to deal with appointed distributors only. It defeats the purpose of the supply chain.

A real market scenario during my time...

The printers market is so competitive in msia and major brands face tough market to supply to major tender customers from parallel importers.

yes, then it is not "The fault lies with the manufacturer for appointing a wholesaler in China." then

Basically you're suspecting that they're operating illegally i.e. no proper permit, license, procedures or approvals. Yes, you can report them if you have sufficient prove. If you even know that their foreign workers are working without permit/visa, can even report to Immigration Department. If you know that their premise didn't apply for business license, can also report to the local Majlis Perbandaran.

need to check with the IP Lawyer.

coz mine last time, the principal hired the IP lawyer and work with my side.
our issues was parallel import and fakes (petaling street)

I'm not saying the company is illegal. If they're not getting the proper approvals, that means part of their operations is illegal & that part can be reported. So, you can proceed with reporting them.

it is not exporting to sell in Malaysia...it is they sell in China, then the buyer in china sent to Malaysia

yes cannot solve as can be seen from many other parallel imported goods in many other countries too.

i think,
it is not the manufacturer's supply chain issue...the supply, demand and distribution has no issue
it is the "globalization and entrepreneurships" of people.
where ease of communication, transportation and the availability of internet for info seeking and sharing do play a part

I dun understand how those ppl can buy from China and resell to Malaysia at cheaper than TS sole distributor price in Malaysia? Unless TS not getting best price from brand owner?