Still being charged for a full month after cancelling

I had 3 lines with AT&T Small Business from May 2016 to December 2020. My account is located in California. I was planning on switching over to T-Mobile so I called AT&T multiple times to cancel my account prior to my billing cycle ending on December 2, 2020. I could not get anyone to talk to! 

Dec 1 - I went to my local AT&T store to see if they could help. I was told that they can't cancel accounts in store and I would have to call. I mentioned that I am switching over to T-Mobile the following day and asked what would happen if I end up cancelling my account after my billing cycle ends on the 2nd. He said that my bill would get prorated for the days my account is active. 

Dec 2 - I went to T-Mobile, got 3 new phones and ported over 2 out of 3 numbers, effectively removing the 2 lines from my AT&T account. Later that night, I logged into my AT&T account to remove my credit card from autopay. I also see that there is only 1 number left in the account.

Dec 4 - My daughter (in the east coast) went to T-Mobile, got a new phone and ported out her AT&T number.

**At this point I am expecting to receive a bill reflecting a prorated charge for the 2 days my daughter’s number was still active on my AT&T account, based on what I was told.

Within the next week I receive a bill issued on Dec 2 for $188.46. This bill was for Dec 3-Jan 2 service and only included the 1 line that was active until Dec 4th. My monthly bill has been $210.11 (with 3 lines) for the last couple of month prior. Now I understand that the bill was issued prior to the line getting disconnected so I thought that the bill just didn’t reflect the updated prorated balance. 

Dec 14 - I call customer service and spoke with Glendale. I told her the whole story and she claimed that my bill of $188.46 was for the previous month’s service (Nov 3-Dec 2). I told her I am fully paid for that month and the bill I was talking about clearly says Dec 3-Jan 2. I ask to speak to a manager but Glendale just offered to lower the bill to $90 but I felt that wasn’t right because the line was only active for two days, and I was told that I would only pay for 2 days worth of service.

Dec 19 - I visited the AT&T store to see what they can do. I brought all my bills from the last few months and the current bill of $188.46. They reviewed my documents, said that AT&T bills in advance, and they agreed that I shouldn’t be charged $188.46 for Dec 3 - Jan 2. They said I need to call again and say that my bill should be prorated to reflect only charges for Dec 2 - Dec 4.   

Dec 23 - My credit card is charged the $188.46 through autopay even after I removed it. I disputed charge with credit card company and they credited my money back to me.  

Dec 29 - Called customer service again and got passed around for hours. I spoke with 3 different people only to repeatedly be told that my bill was for the previous month. NO IT'S NOT.

Sometime in early January - I called again and waited hours to get a call back. A man finally called me back and promptly HUNG UP ON ME after I said I had a question about my bill. (Edited per community guidelines)! 

Jan 22 - Tried calling again but couldn’t speak with anyone. 

Jan 27 - I received a letter from AT&T stating that my wireless service has been cancelled (don’t know how there is a service to cancel with NO LINES connected) and that my account will be referred to a third party collector if it remains unpaid. 

Every time I try to call I either get wrong information, get hung up on, or don’t get a call back. I don’t know what to do anymore. I’m posting here hoping someone might be able to help.

I’ve done some research and I see that apparently AT&T doesn’t prorate. But WHY would SEVERAL AT&T employees tell me that they will prorate??? And why, from the numerous “customer service representatives” I spoke with over the phone, was the issue of prorating never brought up? I was only told that I was being charged for the previous month. I have NEVER been charged for the previous month. 

Is there a direct number I can call for someone who can actually help? I am tired of being on hold and transferred around for hours, only to be hung up on :( I just want to settle this before AT&T negatively impacts my credit.