I went to Maxis counter which located at Velocity Mall this evening (20/10/2018) at around 5pm something to purchase Maxis Hotlink prepaid 6GB, 30 days data plan.

Initially I top up RM30 as the Hotlink Red showing got promotion for the 6GB, 30 days plan with the price of RM28. After top up, I checked my Hotlink Red app and it shows the balance of RM27 something instead of RM30.
The staff there explain to me that there was SST charges for the RM30 top up and I was OK with that explanation.

Therefore, I was going to top up another RM10 again to ensure that my balance is enough for me to purchase the Hotlink Prepaid 6GB, 30 days plan, but before I manage to top up another RM10, I saw my balance was auto deducted from RM27 to RM23 something. So, I immediately reported this issue to the staff there to help check, so while the staff checked for the issue, then I found that my balance had deducted again from RM23 to RM20 something.

OMG, what is wrong with Maxis Hotlink system, they robbed my prepaid credits in front of me. I lost RM7 within 3 minutes.
The staff there told me that I should turn of my phone data during the top up. This is ridiculous.
Imagine if I top up RM100 in my prepaid account and purchase the mentioned Prepaid 6GB, 30 days data plan now. After 1 month it expired and if I didn't notice that or I was too busy to top up and renew the plan immediately, with the speed of losing RM7 per 3 minutes, what will happened to my remaining balance?
This totally doesn't make sense at all. How can they deduct my prepaid credits without my permission?

Then i went to hotlink portal and sign in an account there to check the E-Statement and found out this:

20-10-18 16:32:28 Special Rebate 00:00:00 Special Rebates RM1.70 RM 30.06
20-10-18 16:34:13 GPRS 00:01:33 Data RM10.00 RM 20.06
20-10-18 16:45:06 Special Rebate 00:00:00 Special Rebates RM0.57 RM 30.06
20-10-18 16:49:25 6GB/30 days 00:00:00 MI Purchase RM28.00 RM 2.06

I was wondering, what is this GPRS that cost me RM10? When did I request for this service? I was trying to renew my 6GB, 30days data plan, why should I request for this GPRS?
so ends up I spend RM38 for the 6GB, 30 days data plan instead of RM28 as they offered.

I demand for a refund on this.

what should I do? any advise?

I'm afraid u don't understand full story,
even if u disable mobile data all the time,
and disable Wi-Fi assisstant (which will automatically switch between Wi-Fi and mobile data while Wi-Fi is weak) ,
it still charging RM0.10 until the money is depleted.

Something is wrong at their server site for years (we had heard alotx of these stories in years), and it keep happen and happen again.

Since hotlink removed the  e-statement website login from their hotlink website last year,
something like this is expected more and more...
coz, sb who was using website to check thier e-statement, was forced to put their simcard into smartphone to check the e-statement, and that may trigger the mystery RM0.10 charge anytime even without their notice..

yes, and no.
when u will get it ,and u get it.
Even u use the same phones and same habit for years (or even decade) without issue,
suddently it just showing up..

I also a veteran hotlink user with multiple phones.
I can very sure that there is something wrong in their system that will trigger the RM0.10 gprs charge.

changing your phone setting or habit is not an good option, I'm afraid.
they should improve their system.