Product: Credit card or prepaid card

RE : CitiCard XXXX XXXX XXXX credit card. Despite a transaction dispute in process with an XXXX seller regarding my {$540.00} supplement purchase ( on XX/XX/2017 ) as product I received was not what I ordered and was returned, CitiCard processed this {$540.00} charge through my XXXX account without advising me of seller 's claim and allowing me to dispute the claim before CitiCard processed the {$540.00} payment to seller through my CItiCard XXXX account. CItiCard simply notified me that the {$540.00} payment had been processed through my account after the payment had already been processed by CitiCard. Both XXXX and seller ( XXXX XXXX XXXX ) agree that the {$540.00} is due to me and both XXXX and seller state that the {$540.00} refund has been processed back to my CitiCard XXXX account. CitiCard, however, denies that a refund has been received and is not only billing me for the {$540.00} charge but has now added both late payment fees and interest charges, despite both XXXX and seller acknowledging my return of the incorrect product I received. CitiCard said that I ( rather than CitiCard ) must contact XXXX and seller to obtain the {$540.00} refund that XXXX and seller state has been refunded to my credit card but CitiCard denies receiving. I have communicated in writing withCitiCard and with both XXXX and the seller more than 60+ times during the 6+ months since the XX/XX/2017 transaction date and both XXXX and seller state adamantly that a full refund of the {$540.00} payment was processed back to my XXXX account ; however, CitiCard continues to deny receipt of a refund. An XXXX supervisor asked if, in addition to my efforts, CitiCard had also submitted a claim for the refund? The XXXX supervisor was unable to find any documentation of any claim submitted on my behalf by CitiCard with these records. The XXXX supervisor advised me that the various banks have their individual procedures for submitting claims regarding disputes such as this. Despite the fact that CitiCard processed this {$540.00} payment through my XXXX account when a transaction dispute was in process without advising me of the nature of seller 's claim and allowing me an opportunity to dispute seller 's claim and only notified me of the processing of the payment to XXXX after the payment had been processed, CitiCard continues to respond that it is my responsibility to follow up on the refund that both XXXX and seller state has been refunded to my XXXX account. Although I have requested that CItiCard provide me with a copy of any claim made by CitiCard to XXXX to resolve this matter ( if any claim was in fact processed by CitiCard ) I have had no response from CitiCard to my request to CitiCard for a copy of any claim CitiCard may have processed to XXXX. I am XXXX years old and have worked hard all my life to maintain excellent credit. I pay the full balance on every credit card ( or any other billing ) immediately upon my receipt of any billing statement. I have copies of my more than 60+ communications to both XXXX and to seller as well as to CitiCard over the past 6+ months attempting to resolve this matter. I have provided CItiCard with documentation from both seller and XXXX that the product was returned that that both seller and XXXX agree that a {$540.00} refund is due to me. I have been unable to find information regarding how credit card providers such as CitiCard are regulated and I am urgently in need of help. I simply can not even sleep over this matter that is threatening to destroy the excellent credit I have worked to build and maintain throughout my entire life.