customer service at its worse

I recently received notification that I somehow have a remaining balance with you even though I transferred my number to tmobile years ago. I called to find out what was the date of my cancelation. First rep told me dec 2025. I explained to him thats impossible since been with current carrier for years. I asked for a supervisor, 15 min Later Saed answers, tells me he is a sup and is going to look into my acct. After 2 min on hold he transfers me back to the cue for another rep that I have to explain again to get another supervisor.  Ava answers and she is a sup that tells me now that unless I know the last 4 digits of a cc that was on file years ago and is not even valid anymore she cannot open my acct. After 38 min on the phone and going nowhere. How many reps does it take to give an honest answer of a simple question?