Hi guys can you please help ,

I have had the clutch replaced on the vehicle ,the clutch was a sealed unit
where it has the flywheel riveted to the pressure plate , it was installed by a local mechanic , but when i got the car back the clutch pedal took very high up when released , it went fine for 2 weeks then started to slip

The vehicle was taken back to the mechanic and it was told to me that the clutch plate was faulty and everything was restriped and a new sealed unit was installed , but the same happened when i got the car back , the clutch still took very high up and yes it took
one week for it to start slipping again , what to do now , certainly i cannot see that it could be the clutch seal assemble as it is complete as a unit , could the mechanic not have overlooked something .
can you please help me with suggestions where ells i can start to look at .

all help will be appreciated
many thanks Billy