Prepaid Account in collections???

I was on auto pay and didn't have money in my bank account when the payment went through. My bank rejected the payment of course and AT&T cut my phone off. I used wfif calling for a couple of days after it was cut off and when I got the money to get it back on att prepaid wouldn't let me on the app. Said my account is in collections and I had to call a certain number to resolve it. I call customer service and they would not allow me to speak to anyone but the "collections department" so they put me on hold and a computer says they are closed until Monday. I tried to pay on a Saturday. So I can't talk to anyone and I can't pay my bill to turn my phone back on. There is a chat feature on the app and luckily I was able to chat with someone, he told me to go to an AT&T store and pay cash to get my phone back on. I did. And it was cut back on. I paid $69 cash. Still I was not allowed in my account so that follwing Monday I call the "special" number they would only allow me to talk to someone on. The lady says I had an echeck returned and I owe $80 how would I like to pay. I told them I just paid to get my phone back on at the store. The lady said I had to pay for the services used. Mind you it's prepaid so I didn't use any services only wifi calling and when I got my phone cut back on at the store after paying. She said I owe it and would not let me talk to a supervisor, said they were busy. I do not owe them anything except maybe the return check fee. But I shouldn't have to pay $80 for a phone bill I didn't even use. They cut my phone off. I'm not understanding their logic and they will not explain anything to me. Why I have a bill in collections is beyond me because it's prepaid, I pay before I use the service. I didn't use their service until I paid cash at the att store. Fortunately for me and unfortunately for them I unlocked my phone and am going to another carrier in the morning. They even had the audacity to not let me take auto pay off because they won't let me in the app or do anything on the phone until I pay them $80. Not happening. So I had to pay my bank to stop any further payments from att which means they lost a very loyal customer. It (Edited per community guidelines) and I feel very unheard and mistreated. Has anyone experienced this? Probably not.