A tip for everyone.

The next time whenever you apply for a credit card, take notice of a clause which goes something along the lines of "Allowing the bank to use your details for internal marketing purposes / 3rd party marketing purposes." You will notice a check box beside those clauses which may indicate "Yes" or "No".  This is of course up to everyone prerogative whether they want to say yes/no and obviously if you decline, the bank have no right to reuse your personal details for their marketing purposes.

Thus effectively stopping them from reusing your details to perform cross marketing of their products.

Do not despair for those still wanting to remove themselves from such list - write to the bank.

Take note that the above is one of the protection of the PDPA (Personal Data Protection Act). If the bank violates it, you may report it to the PDPA authorities for legal action. The same can be applied to those pesky telemarketing calls. Next time if you get one of those calls, ask them where are they from (note the company, time of call and person who is calling) and ask them where they get your details. Then ask them whether they have written consent from you to call you. See their reaction next.

Similarly, you can ask them to remove your information forever from their database. Non-compliance will be reported to the PDPA authorities.

That should be it. Note that PBB email channel are not the most efficient in the world.
Try to google some ideas on how to write it effectively - effecting/invoking the data protection portion. The bank will get the hint if you write it correctly and there's no element of threats needed to achieve this.