Probably not, since they probably want an NRIC for the upgrade process.

But why would you want to use the same account anyway? Might as well have it under your name in a new account since it's going to be a fresh 2-year contract anyway.

I think you should go to a TMpoint in person and do a cancellation of the previous account. Bring some proof that you are the owner of the address, and tell them you wish to cancel it. You should do this so that your address is not blackmarked, which may cause problems in the future.

At the same time, just apply for the Unifi package under your name.

You may be able to do it through the phone if you can't spare the time to go to a TMpoint, but it may be easier to sort everything out in person, especially if the previous account has some outstanding amount to be paid. You don't want to pay it after all.

Is it confirmed only one port available for your house? After I registered my UniFi, my housemate also registered hers. So there are two active lines here.
The problem now is how to cancel the existing one...

That's where I think the problem could come from when I suggested that you go in person to a TMpoint.

I believe the moment they put the application address into the system, they will see the existing one. That's when you may have to clarify that you're both tenants and he has gone missing, and you don't want to be responsible for any outstanding amount he may have.

If you are unlucky, you will get a straight 'no'.

If you are luckier, you may be asked to speak to a more senior person where you have to 'cerita panjang'. Hopefully, he or she will be sympathetic and will help you resolve the situation, but may want to see some tenancy documents.

If you are really lucky, it will just get approved and they resolve the logistical mess themselves.

I think it's worth a try in your case, since you have nothing to lose. 

I still don't suggest doing it through the phone. The frontline CS personnel there mostly don't have the authority to deal with messy cases.

Good point... as long as there is nothing outstanding that they want you to pay up before doing the upgrade 

Again, it's worth a try, resolved through an agent or otherwise. They may be desperate enough to want the extra monthly subscription coming in and overlook all the discrepancies