Product: Money transfer, virtual currency, or money service

I want to make a formal claim against PayPal Credit for cashing a check on XX/XX/XXXX for {$1800.00} issued by my bank ( XXXX XXXX XXXX  ) and not crediting my 'PayPal Credit ' account for which it was issued. 
I have a credit card with the XXXX XXXX XXXXXXXX and, as we all know, commercial banks frequently offer 0 % interest for balance transfers from other credit cards with higher interest rates. XXXX XXXX  XXXX offered this 0 % interest balance transfer in XX/XX/XXXX. 
I also had an account with 'PayPal Credit ' for my purchases. 
I wanted to use XXXX XXXX XXXX XXXX offer to pay a portion of my PayPal Credit balance at the time and I requested XXXX XXXX XXXXXXXX a {$1800.00} balance transfer for the PayPal account charged to my XXXX  credit card. 
XXXX XXXX XXXXXXXX issued a check for {$1800.00} and sent it to PayPal. The check was received and cashed by PayPal on XX/XX/XXXX, I have proof of it, but never credited to my PayPal account. 

DETAILS : In XX/XX/XXXX, XXXX XXXX XXXX XXXX XXXX ) offered me a 0 % interest balance transfer to be charged to my XXXX credit card. At the time, I had a PayPal Credit account balance and I decided to use XXXX offer to pay off some of the PayPal outstanding balance. I provided XXXX with all PayPal Credit account details and XXXX issued a check ( No. XXXX ) dated XX/XX/XXXX for {$1800.00} and sent it to PayPal. The check was received and cashed by PayPal on XX/XX/XXXX. 
After a reasonable amount of time, I checked my PayPal Credit balance and noticed that {$1800.00} had not been credited. I called PayPal Customer Service, after many questions, the representative indicated that the above mentioned check had not been received. 
Next, I called XXXX and they confirmed that PayPal had in fact received and cashed the check on XX/XX/XXXX and a photocopy of the check was provided. ( photocopy to be provided upon request ). 
Since then, the long and tiresome phone calls and inconsistent responses from both sides began. Both entities kept sending me back and forth indicating that I should deal with the other one. 
In the meantime, PayPal accepted and issued a credit of {$1800.00} they said while the investigation was undergoing. However, they also indicated that they may reverse the credit if unable to locate the payment, which in fact occurred. They did not find the payment and reversed the credit. 
Throughout the year XXXX and part of XXXX, I made many calls to both entities and the answer was always the same. I managed to get an appointment for XX/XX/XXXX with a XXXX representative, XXXX XXXX XXXX at the Branch in XXXX, XXXX VA. The meeting lasted for about two hours during which the representative made several phone calls and finally said that there was nothing XXXX could do because they had proof that the check was received and cashed by PayPal and that, for them, the case was closed. I asked XXXX XXXX to provide me the outcome of the meeting in writing. XXXX XXXX indicated that he would send me a letter in that sense but a formal letter from XXXX was never sent to me. 
I waited for months to be contacted by either party, hoping that any of them will finally locate the funds. No one contacted as of today. 
To avoid damaging my excellent credit, I continue making monthly payments for the {$1800.00} I never received. This event has caused me a great stress and tremendous financial loss. 
I am XXXX XXXX XXXX and trying to save money for my retirement years and I can not afford to lose this money. Thank you.