Opening a dispute when the amount was paid over time
I made a purchase in January (needlecraft supplies) and was told I could pay over time, as it takes awhile to get everything from suppliers. I paid over time and finished on the 17th of May. The seller is still telling me the supplies haven't arrived. I feel this is long enough and want my money back. But when I go to enter the total, it won't allow me to enter more than one payment. What do I do now??