Why was i sent to collections for a cancelled plan?

I've been an xfinity customer since 2016.

1) I was sold an incorrect xfinity mobile and home internet package deal which i was supposed to get discount on. I never got this discount. After months of chatting with xfinity assistant (India workers, they don't care nor do they know anything about your contracts and they disconnect the chat when asked to do something) During this time, i contacted xfinity many times. they told me the discount is coming, one month, two months, next billing cycle, etc. never came. 

2) after months of dealing a specialist was finally assigned to me. they finally realized that they sold me the wrong deal and asked me to send the ipad back on my own dime. I sent it back, and they called me back to confirm that its been returned. I gave them the tracking etc. the specialist then confirmed that they will refund me of all my charges and will dissolve my account. But once the ipad got returned, the specialist disappeared because xfinity does not allow us to contact certain people, they have to call you. they never call you. 

3) now because the ipad was returned, my home internet bill went up, i was ok with this because at least i was past dealing with this issue. 

4) after a couple of months i kept getting billed for my mobile service (ipad returned, i dont have this anymore, i was told account dissolved) 

5) i kept calling xfinity and finally got someone who said the account was left open - they dissolved my account said nothing owed and i can put this past me. 

6) i kept getting charged again! I dispute my charge at this point with my bank because no one at xinfity can help me here. I even went to the store at this point many times and the store manager himself told me that there is nothing that I can do.

7) Xfinity now has reported me to collections and my credit score dropped by 80 points. 

I have chat transcripts, emails, and call recordings of my accounts being cancelled and dissolved. 

I am on the phone with xfinity now, and they are saying there is nothing they can do, go call legal. WOW. 

Update 1: went to the store to get pictures and print outs of my account which shows account paid in full and 0 owed. 

update 2: got a callback from xfinity and they transferred me to “legal” a middleman company who send a letter to this address and they will send it to the right company.