just sharing my experience.

Early of Apr 2019 i apply for upgrade 2 card gold to plat.
MBB CS1 request to fill form and submit via email to card center as new application. CS1 promise to transfer everything (outstanding balance, TP) to new card once success approved & cancel the existing gold card.

took a week to get approve and another week to received physical Plat card.
observe from M2U, system does not auto cancel the gold card and transfer everything like CS1 said.
call MBB, CS2 told me cannot make such transfer really piss me off. once cancel gold card all TP will burn.

after few day, i decided to use TP to offset SST and call MBB.
while chating with CS3, i try luck to request again on what CS1 promise.
CS3 able to do the transfer for me without saying anything and cancel the gold card.

my advise is try few time with different CS before give up. you may meet the right one.
and basically CS can do the job, sometime they just dunno or not willing to.

last week i renew through Etiqa website, payment by Amex is accepted.