I'd recommend you speak to the motoring ombudsman.
Also you might be covered under consumer law:
Your consumer rights within six months
If a product develops a fault within the first six months after purchase, it’s assumed it has been there since the time of purchase. This means it’s up to the retailer to prove it wasn’t there when you bought it.
If a repair or replacement has failed, you have the right to reject the goods for a full refund or price reduction.
https://www.moneyhelper.org.uk/en/getting-help-and-advice/consumer-rights/consumer-rights-what-you-need-to-know