Sounds like you bought a lemon, did Grieves not say anything about the fact that you brought the car back a month after changing the last clutch?
I have used Grieves a few times in the past 5 to 6 years since I had my last impreza and now since my brother in law had his P1 which I helped him maintain. I have found them very helpful in the parts department, although I have only used them once for the service department, to get the P1 keycode reset, they were decent enough and all the staff seemed really helpfull anytime I've been in.
Sorry to hear you have been so badly stung but surely some alarm bells rang when you had to replace the clutch in the space of a month? If you have not already done so I would suggest going back to Grieves and give them the opportunity to put things right?
Just my humble opinion.