I am not sure if your motor has a dual mass flywheel but these can cause problems you are experiencing,they are usually very expensive and a lot of people convert now to a solid flywheel,have had plenty of new faulty clutches so I wouldn`t rule anything out but it looks like your g/box will have to come out again for a look,if the garage didn`t replace what they said then you will have to take that up with them.
cdc, December 2012