Can tmobile block my iPhone?

I have an iPhone and the bill is to expensive and tmobile customer service is rude and ignorant and don't help me. I'm going to get a prepaid sim card for the iPhone that I have. But since I'm not paying the bill can they lock my iPhone?

Yes they can block it
you will have to change number and sim card then it might be a bit harder to block

If have a contract then your phone will be locked if you change the sim
if have buyed factory unlock mobile by paying full money then they can't lock it

I think that once you change your SIM card to a prepaid one, they can't mess around with it. If you're not paying the bill, they can block the previous SIM card for sure.