Not able to cancel t-mobile home internet nor turn in router anywhere.

Surprising I was in a store in Florida and I saw a lady bring her modem back in and it took about 30m  , I was there to buy a phone, I wanted to ask her why, because I just got a T-Mobile modem 4 days before, but it looks like she could not speak English. I did not see any issues with the return.

How is my service working?   10 days now and two outages.  I only called once and they said it was congestion, but I reminded him congestion is not a 2000ms ping and zero download is an outage, He did agree and took my connection down and I restarted my modem, and all is well, the second outage is unknown because I was leaving the house and did not call.

He did say even during congestion I should get 33m per their practice.