You're covered by law and the consumer rights act. Ask them to fix it, if they refuse take them to court. A quick search on which? website brought this up hope it helps;
When you take your car into a garage, it's protected under the law of bailment, which says that anyone you entrust with your property has a responsibility to take reasonable care of it.
If they fall short of this, they're responsible for any damage or loss incurred while your car is in their possession.
In addition, the Consumer Rights Act (which replaces the Supply of Goods and Services Act from 1 October 2015) says that your garage must provide its service with reasonable care and skill and will be responsible for any damaged caused if it doesn't.
Garages might display notices denying responsibility for loss or damage to vehicles in their possession.
But under the Consumer Rights Act, which replaces the Unfair Contract Terms Act 1977 and the Unfair Terms in Consumer Contract Regulations 1999, these can't be used to try and take away, limit or restrict your legal rights.
Whatever the cause, it’s very unlikely that a court would uphold a garage’s claim to be exempt from all responsibility.
Should your car be damaged, you can claim compensation for the loss or damage and potentially, reasonable expenses incurred as a result, such as the cost of alternative transport while your car was off the road.
Before incurring such costs, give the garage a chance to cover them or help with your arrangements.
