Poor workmanship - leaking shower fittings less than 12 months old

What can I do - Dean Oxlade of 3 counties heating/plumbing converted my bathroom to a shower in May 23, the shower fittings are now leaking and the the water is ingressing into the wall, what do I do, please? i have sent him a text as he said emails are a problem when i needed him to fix a previous problem. I have sent him a text as he said it is the best contact medium. I will take legal action to cover costs to get it repaired.