Unfinished plumbing work

I used a plumber recommended by the firm I purchased the bathroom goods from. I stupidly paid him in full but now have problems with the shower screen and him not connecting the shower. I have written and phoned and left messages all to no avail. 1) Is tis a case where it is a Trading Standards issue 2) Can I write and say that I will get another plumber to finish off and charge him through the small claims court
The bathroom place seems to have closed down but I am writing and enclosing a copy of the letter I sent to the plumber
The tenant is complaining
Any other suggestions