After almost 12 months you are not entitled to a refund.
Unless the fixing is defective then they don’t have to repair it either. Assuming it is defective they are under duty to repair it.
However the practicality and legality are different if they simply refuse to do so. Then you are faced with getting it repaired yourself and sueing them for that cost in small claims court.
You can easily issue small claims court proceedings here www.moneyclaim.gov.uk
However be aware that if the seller is not a large company the proceedings will usually be transferred to their local court which might not be convenient for you