I made a purchase and had item shipped to me. On arrival it was not what was advertised...

I made a purchase and had item shipped to me. On arrival it was not what was advertised so I requested a refund that seller accepted without issue. I printed the label and shipped item back to seller. Seller even confirmed item arrived. Offerup two days later tells me the refund expired and was not issued. All the responses so far from Offerup are canned logout then login to resolve the technical issue. Absurd that they don't have real support. I guess the only recourse is to report fraud to my credit card company