They keep on wanting my money but refuse to help me with their faulty/mouldy kitchen sink which I bought in January and reported the fault the next month in February

They keep on wanting my money but refuse to help me with their faulty/mouldy kitchen sink which I bought in January and reported the fault the next month in February. I’ve went there, sent emails for six months whilst paying my monthly instalments in full without fail. I decided to no longer pay until they replace or take the sink and refund me. A sink can’t absorb water and be mouldy in less than a month of purchase