Gutters not installed properly

Ironman Guttering installed gutters on my property in August last year. I was generally happy with the work until it rained in October and I realised one of the downpipes was not draining water. Fir the reason the overflow from one side is damaging my garden furniture. I informed the company and they have made promises since January to come fix their mistakes but to date they have not come. I have proof of watsapp messages send to the owner. I am not happy at all. Please help