Air-Con leak found after test, re-gas and antibacterial treatment

Hi all

A couple of weeks ago I had my Ford Fiesta air-con tested, re-gas and antibacterial treated. Yesterday I had it serviced by another garage. They say that the air-con has a leak. I phoned the original garage who are going to have a look at it next Monday, but are charging me for it.
Does anyone have any advice on my rights? In my mind the leak should have been found during the testing.

Any advice gratefully recieved.

Mart6049