Improvements Would not issue refund West Chester Ohio

I purchased two sunshades from Improvements and I returned them as they would not work properly. I was issued a gift certificate.  When I contacted Improvements I was told they would void the gift certificate and would issue a refund to my credit card. I later contacted my credit card company and found out that no credit was issued. I then called Improvements again and they said the gift certificate was all they could do as I had not returned the shades within 90 days of the purchase date. I do not want the gift certificate as I do not plan on purchasing anything from Improvements ever again.