Client asking for a refund after 3 months the contract has ended.

[reymundjamito]

Hello,

For full context, I worked with this client in May this year. The job is to create a product. I have successfully implemented the functionality in a readily available product for prototyping. I told him from the very start that I can't do software and only the coding for the hardware. He still hired me. We agreed on hourly basis and per milestone for the project. I was able to do the some milestone that I discussed with him and he was happy of the result. I told him that there was a lacking feature on the prototype and I can't do it. It's out of my expertise. I didn't charge him for this. I will only charge him for manual hours if I can give him results. He hired someone else and I told him that the guy is much better than me and he can hire him to finish the job. I quit.
He ended the contract last july  31. But we still have communication after that because I was still trying to help him.

Fast forward to Nov. 7, 2023. He is asking for a refund. I messaged him in upwork that we need to talk about this. He replied to me and then blocked me. Now I can't talk to him. I didn't tell him explicitly that i will not refund him. I was going to until he blocked me immediately after sending reply.

What should I do?