Product: Checking or savings account

On XX/XX/2021 we made a check deposit at the counter at the branch for {$26000.00}. 
The check came from a customer in XXXX but the funds and the account were in USD. We have done business with this customer for years. The check said " USD Account '' On XX/XX/2021 my accountant noticed a " Adjustment/Correction of Posted Item '' transaction for minus {$6500.00} There was no explanation on that transaction and it shows as Uncategorized. 
My accountant called Bank of America customer service at XXXX. The Bank of America rep said that there was a note on that adjusment that said " Sorry for the inconvenience, the amount of the counter credit was different from the check ''. But the rep admitted that the amounts matched so she was confused. When asked what we could do about it she said I would need to call ( as the signee ) to open an inquiry. I was in a meeting at the time but told my accountant to call and then put me on the line if they needed me. So my accountant called the bank again at XXXX and spoke to a different rep that was able to file the dispute in the system without speaking to me. The rep said she did not see a reason why we would not get our money back. She said that in 3 business days we would see something, but that going to the branch might resolve it quicker. 
The request number was : XXXX Online it showed : Open XX/XX/2021 We have received your submitted case and it will now be assigned for resolution On XX/XX/2021 at XXXX my accountant went to the bank but was told they could not help him and that I had to come in since I was the signee. 

I logged in to Bank of America and noticed that the request showed Closed now : Closed XX/XX/2021 We have completed your request. Please call us toll-free at XXXX if you need specific details regarding the resolution. When you call, please have your account number, which you can locate on your Account Details tab under XXXX XXXX XXXX. We appreciate your business and look forward to serving you. 

At XXXX I called Bank of America XXXX XXXX XXXX XXXX. I spoke to a rep for 28 minutes. She looked at the transaction and said that the correction was due to a currency conversion. Unfortunately she dropped the call when she was transferring me to another department that was going to help me. 
I took advantage and called the customer. The customer confirmed the check and the account were in USD. 
At XXXX I called Bank of America again. I spoke with two different reps for 1 hour 39 minutes. The last rep said she didn't see anything about currency conversion on the adjustment. She didn't know why the previous request had been closed and opened a new dispute. I told them I needed the money to be put back into the account while they figure out what was wrong in their system. She said she couldn't do that. 
I did not see the request she said she entered ever appear in the Message Center online. 

On XX/XX/2021 at XXXX I called Bank of America again. I spoke with a rep that said again that he didn't know why the dispute had been closed. He opened a new request. He said he didn't see anything wrong with the deposit, but that the department that entered that transaction was the back-office and that there was no way to directly speak with them. I asked for the request number and was given XXXX. I told the rep I didn't know what else to do, that I felt helpless since I could not talk to anyone that took responsibility or could explain the transaction. He empathized and said to wait 3 to 5 days and hopefully it would get resolved. 
After the call I noticed that request number appeared online in my Message Center. 

At this point the bank has taken {$6500.00} without explanation and 6 days have passed. It's a lot of money to just go missing without an explanation as to why. Nobody is willing to put the missing money back in the account or take responsibility for it and they blame the " computer system '' or the " back office '' for the mistake.