Return Fee and TMOBILE has equipment

Spoke to supervisor Leti she stated that I missed the return deadline for a internet modem and I would be charged $230 for a non return fee. However they have the modem and are still charging me for. Backstory, I received a modem for replacement and it didn't work either. Several weeks later they sent a power cord which helped and I kept the original modem. I sent the replacement modem back a week or 2 later and they stated that I would receive a credit to my account for the return fee. Needless to say I'm still being charged for it after being told by 3 different representatives that it would be removed. I will be leaving TMOBILE this week