Business account overcharge - Despite 5 months of phone calls, overcharged $900 even after renewing a contract

I managed our building's small HOA and our contract was up for renewal in August of 2023.

• July 2023 ---> I called to renew and it was aligned and accepted: Ref ID: C34727672
• September 2023 ---> I then noticed that my bill increased and it stated that I was no longer a contract customer so was provided a monthly rate ($640 vs contract of $220) which was 3 times the contract rate.
• September 2023 ---> I called twice, and in speaking with 2 different representatives, I was told they cannot fix this now, and it would need to go through the back office and would reflect would be corrected and I would be reverted back to my contract rate. ID: PRY3YN5 'Claudio'
• November 2023 ---> I was charged again, the month-to-month rate (nearly $800 dollars) and was given a late fee to boot

I called and spoke to 2 more representatives, who repeated the process: 1) Open up a 'case' with the back office 2) back office will contact you when they analyze your account 3) You will get a credit on your account

I have heard the statement by so many representatives, I can repeat it back to ATT verbatim. 

Can someone please help correct this mistake, I have now spent about 8 hours on this, have never had a worse customer experience across any industry.