Citibank Credit Card Complaint

Citibank Credit card department,

Transaction issue Minnesota

I made 2 online purchases of phone refill cards for - that were represented to give me 6 months of phone service for each card. I did received 2 phone cards but they were never activated /paid for by the seller. In other words I paid for 2 cards with zero value. In order to use the cards, I would have to pay the money all over again. I disputed the charges but Citibank denied the dispute since I did not return the cards to the seller. The seller never responded to my request for a return so that option was not available to me. - confirmed that the 2 cards can be used once they are paid for as the seller never paid fr these cards at -. The total amount lost was $420.00. I do n't understand why Citibank would not support my claim.