That's because you called to the wrong office. You need to call the relevant government department to waive the credit card service tax. HSBC is acting as the collection agency to collect the credit card service tax for the credit cards issued by them on behalf of the government.

Goodness.
GST is collected by the banks on behalf of Jabatan Hasil Dalam Negeri Malaysia. You need to call them if you do not with to pay GST and be prepared for a lengthy justification. (I am not joking) Google to get any number to the office which is convenient for you.

   
What Hye Tried to Say that, Paying GST of Credit Card like Paying Your Income Tax to Government You Can NOT Avoid It, You Understand or Not...

GST (Government Sales & Service Tax) can NOT WAIVE or OFFSET by the Bank, it is collected by the Government and the Bank Act as Agent to Government & Collect all from Credit Card Holder, so You have to Pay the Tax...
If Not Paying the GST, You Maybe be Blacklisted by the Bank ($50 per Prinp. Credit Card a Year)

You x Afford the Yearly GST.... Cancel Your Credit Card, go Get Yourself a Debit Card With No GST...EZ 

Myself got 6 Credit Cards, I have to Pay $300 ($50 GST x 6) to Government Every Year....

Let us settle this once and for all...

GST is a tax, all cardholders have to pay, with banks acting as "agent" to collect on behalf of the government.

However, banks CAN give u a cash back, rebate, credit or whatever they may call it to EFFECTIVELY relieve you from bearing the GST.

It's all law; the law states that GST has to be paid by the cardholder, but there is also no law stopping banks from giving customers a discretionary cash back/rebate/credit.

I never implied such it was possible but instead directed to the method known. Success rate was 0%, nobody did it before not LHDN is interested to entertain anyone. The GST problem was aggravated by agents severely impacted to the GST ruling when card applications dived as compared to before. (This will continue as I still hear card agents peddling to date their credit cards with so called GST "waivers" which is misleading, false advertising and unethical)

The problem is actually both ways - public are still spoiled by free cards, freebies (in the forms of gifts & free cash) and in the aftermath rant when they are so called "cheated" by the agents or banks. Unfortunately, the public has a very long way to go before the emergence of a more financially matured society emerges.

All the while GST was by law a requirement to pay.
By your story, you knew it but still you want to attempt not to pay it by coming in here and asking. 
I had so many people reacting people should share when I told them off - This section of the forum is not a place to share how to break laws. Contrary to the maybe some other sections of LYN where they are free to talk about anything they like - truth or fiction.