T-Mobile non return fee on gareway scam

Same thing is happening to me right now. I setup a date to return my modem but it got misplaced and I failed to return it. 2 months later I get a Failure-to-Return fee on my account of $220. The same day I noticed it I contacted T-Mobile and explained the situation, they told me to return it asap and I can get refunded the extra $220 on my bill. I returned it that day and waited a week "per their instructions" and called T-Mobile to get the fee waived. They told me that they would only meet me halfway and pay $110 of the $220 fee.. Why am I being charged a fee at all since you now have the device? The device was only used for a month due to the extremely low performance of the internet service anyway.. This needs a resolution and I see this is happening to multiple people..