Start by checking your rights under the Consumer Rights Act 2015 and gathering proof, such as receipts, photos and messages. Contact the trader in writing, explain the problem clearly and say what remedy you are seeking, such as a repair, replacement, repeat performance or refund. Give them a reasonable opportunity to respond and keep records of all communication. If the issue is not resolved, consider an approved alternative dispute resolution scheme, a card-provider claim where relevant, or further advice from Citizens Advice. For a significant dispute, a solicitor regulated by the SRA can explain your options.