Unreasonable and unprofessional service received.

I found the staff very in professional and un reasonable.

I bought a second hand starter from them for the price of almost a new one . But due to lockdown this was my only option as I am an essential worker. They have ensured me that the starter matches my original one and that they have tested it and it works 100%. I am not an mechanic therefor I asked them to assist in ensuring that I have the correct part. I bought it and took it home to find out that it does not fit my car . Asking to return or refund it . I was refused and said they have a no-refund or return policy. I was very upset and asked if they could not just charge me a handling fee and terurn my original part and my money . They refused and said I can only buy back my original from them to modify the one they have sold me so it matches my car . I feel this is very unprofessional as I am not a mechanic and all i asked was my money back the secind hand part my sold to me is not even damaged or dirty . Its exacly as they have given it to me. I am willing to pay a handling fee but they just refused me. What should I do now? This was my last money.