Very sorry to hear your having problems. I have recently returned my Minibrute and got a refund as I was very dissapointed with the tech support at Arturia. When I first got my Minibrute it worked perfectly apart from the known top octave being sharp. Others had posted about this and as it wasn't too bad I was prepared to put up with it being a VCO based synth.
After a few months of use it started to get worse, becoming more out of tune and starting to affect the notes below the top octave. I opened a ticket with Arturia and at first I got quick replies but then the replies started drying up. I emailed Arturia support 3 times without reply. In the end I got fed up waiting and returned to the store I bought it from. You only have to look on this board to see the posts regarding pots not working, key bumpers falling off,pitch problems, things rattling about inside! I could go on
In my personal opinion the Arturia Minibrute is an awesome synth, it does so much for the money and to be honest I would have kept it if I thought Arturia cared about their customers, which doesn't seem to be the case as you and others, like me, seemed to be given the cold shoulder.
I see the Microbrute is on it's way! Interesting, does this mean the Minibrute will be even more lost, forgotten in the vaults of time?
The irony for me is I get email after email from Arturia about their new products, software/hardware but never the emails I need.
So I hope you do get it sorted and you get the aftercare you deserve, you paid in good faith for a faulty product. The least Arturia can do is have the decency to reply to you and try to rectify your problem.