The tradesman has been paid and there is a big problem with the job!

The bathroom was completed via this site by Bespoke Plumbing and Bathrooms (Doug Rose) from Salisbury, We paid in excess of £11,500 to him. 2 days later there was a serious drip from behind the wall where the shower was fitted and there are a few other less serious items of snagging. Its been almost 2 weeks since the shower leak was isolated and despite several messages, emails, whatsapp's and a letter to his address - we have heard nothing and he refuses to communicate! So much for the 12 months warranty that he was supposed to provide. We are now left having to find someone to put right his work (potentially £thousands as the whole thing needs to be removed) & sort out any future issues ourselves - surely this cant be right! This has ruined our faith in the Rated People site - Can you help please?