Contacting a tradesperson who is not answering after completing work

I used Ultra Rendering to render some walls seeing your recommendations. After about a month ( in Nov 2022) had a couple of issues. Spoke to them and they were going to deal with it. Nothing heard despite phoning and emailing. You still have 5 star reviews on your site and quite recent ones. Have been waiting 6 months and nothing and trying to contact for 2 months and nothing. What do you recommend?