Car dealers do not have the best reputation for after sales service.
Write a formal letter to their head office listing the faults. Say that as motor traders, they should not have sold a car with these faults and that they are legally responsible for fixing them. You require a refund of the £90 and you are giving them one more opportunity to repair the faults. If they have not done so within 14 days, you will get the car repaired elsewhere and sue them for the cost plus damages without further notice.
You'll find a sudden change in attitude!