Product: Credit card or prepaid card

In XXXX I received a call from discover card stating my account was pass due and in the process of being closed and going to collections. I explained to the representative that I was unaware of any outstanding balances and believed that the card was paid to date. I explained that I recently became aware of severe medical issues and that with XXXX and lock downs had no recollection of the recent charges that caused a balance on the card. 
I explained that the last payment I made showed that I paid the bill in full just as I done before. 
The representative stated that I could dispute the charges and any charges that I did not authorize would be credited to the account and I would not be responsible for the charges. 
The representative then explained that inorder to dispute the charges I would need to set up a payment plan that would prevent the card from being closed. 
I agreed to set up a payment plan and the representative stated that once the disputed charges were reversed any payments that I made would be credited to the account. 
The representative said that it may take longer than normal to investigate the disputed charges due to covid restrictions and regulations have changed during the emergency pandemic, and asked me to please just be patient with the process that she noted everything on the account and that she will forward over to the right department to start the process.

After making the minimum payment for the rest of the year in XXXX and XXXX I then canceled the payment after receiving a letter from discover stating the card was closed. I assumed the matter was resolved and I would get a new card. Immediately after I lost close family members and had forgotten about the letter until recently I was notified that an attorney was attempting to collect the account balance. The charges that I never authorized and dispute in XXXX that i also paid for each month on time over a year on are now being charged to me again. I never received a credit for the payments I made and I was recently notified after calling discover that the charges was never received by their department that I disputed and they are just now being investigated and have 90 days to resolve this matter. 
Mean while I still have their collection attorney attempting to file with the court to collect the unauthorized charges that I paid on for over a year and that discover is still in the process of investigating. 
It appears that discover card has already decided what the investigation of the disputed will be as they still have an attorney attempting to collect charges I did not authorize and paid for as they state they are still investigating the charges. 
My main concern at this point is discover states they are investigating the unauthorized charges and will notify me once they complete their investigation and will provide me with the results within 90 days. If discover is investigating and they haven't verified that the charges are not mine and was not authorized by me. How is it legal for discover to have an attorney attempting to sue me for unauthorized charges that discover hasn't verified and notified me of balance after investigation or credit that they should have issued to me for payments made for unauthorized changes. 
It's important to know that I trusted the representative when they stated they would note the account and forward to have disputed charges credited. It appears they never did until recently. I also request if discover does not credit account for unauthorized charges and credit me for over payments I request discover card bank resolves this matter with arbitration. 

I will forward this report to discover bank and please not this report should also be form of written notice to discover bank XXXX request arbitration of this matter if discover bank is not able to resolved by 90 days. I request all unauthorized charges from XX/XX/XXXX to current be credited to my account and a refund of any overpayments be issued back to me.