I'm receiving bills from a canceled account I already paid off

I created a new account during the Hookup offer period and canceled my old account after a Change of Responsibility, after which I received a hefty $200 bill despite only having 2 lines and 1 free line. I figured that was my last bill for that account, but so far I have received 2 letters from T-Mobile stating a final charge of $137 for my 3 cancelled lines.

The last month they were used was 3 months ago, and were postpaid lines. I don't know why I am receiving another bill, and honestly don't know how to pay it considering the account was cancelled and the link on the bill itself doesn't work.

It looks like I have to call customer support. What are the ideal things to say to make sure whatever rep I talk to understands what I am saying and gets me to the right department, or perhaps waive it entirely?