Disgusting service

I bought a self heating shower unit that cane with a tap attached to the heating system. Ideally, I bought it for my shower at home. When I bought it, I didn't yet have money to have it fitted and installed so it stayed put till I could. Once I could have it fitted, I was told and I witnessed that it wouldn't fit in my shower because of the tap attached to the heating unit. I lodged a return this month because I only had money to fit it this month and noticed it doesn't fit and I asked for them to credit my account instead of a refund so I can buy just the shower head with a heating unit. Now, according to their policy, I am eligible for credit because its not a personal made product and its not a feminine product but its been returned because I didn't lodge a return within 30 days and I didn't ask for a refund, so it should have been processed. What am j supposed to do with this product that won't work at all??