Unknown charge on my bill

I’ve received a bill from Tmobile and charged extra for CellSpot Non Return Fee of $311.40 which I have no knowledge of requesting.

So I was chatting with supervisor and he said he will remove it from bill now and he said it’s done but checking it carefully only $289 was credited and I asked him why and he said good question with long pause saying that late fee has been generated so it will be credited on next billing and refuse to remove it from current billing.

Why do I pay extra money for I didn’t even request it and wait for next month to get credit?

I don’t understand why he can’t cancel the late fee

Probably, If I didn’t qustion the difference then i won’t even get credit.