Yes, I was worried on that too... since my Hotlink app cannot login anymore to check bill. Just to be safe, I called Maxis customer care earlier today to check their billing SOP for port-out customer; you were correct ya, the agent confirmed my account terminated 22 July, and Maxis will send my final prorated bill (21-22 July) around 20th August. No issues with that, will gladly pay it... I just don't like getting unexpected bill haha

If you do not make the calls to Singapore, you should lodge MCMC report to claim those charges. But if you do call to SG, then of course kena charge.