DPF issue and more???

A few months ago the Emission control light lit up along with a glow plug system light which started flashing. I added a solution of DPF cleaner and regenerator and this seemed to cure the problem for a while. Both lights reappeared and so I took the vehicle to a local garage and they carried out a DPF forced regeneration and informed me that it should cure the problem. Upon the mechanics return from his fun with the paddle shift controls along the motorway, he noted that the filter was 0.3% clear and that the Emission control light had gone out, although the glow plug light started flashing again intermittently and could have something to do with the other fault code: P3138 - Intake - pipe airflow control. A few days pass with no lights but then both lights back on again along with the DPF obstructed light ( ironically the latter has never appeared before!!). When I called the garage to explain what had happened all they could say is to ' bring it in for further investigation'. Considering that the second fault code is something that they 'cannot rectify' as it is in there words a code that they do not recognise I was unsure how they were going to proceed. Maybe I should take it to a German car specialist - just not happy at all because instead of sorting the problem out they seem to have made it worse - oh and also it's not changing up into 4th gear until I hit about 2500 rpm?!?! Any suggestions please? The car is an Audi A3 2007 , with about 86000 miles on the clock.

Thanks for your reply. I was considering going down that path. I was annoyed with the fact that only after doing a total of 300 miles since a forced regeneration was carried out, the actual DPF warning light came on for the first time ever. It was explained that a forced regeneration was not a guarantee and if it it was, would only last for between 1000 and 2000 miles, and therefore driving under the same conditions - short journeys would lead to a another build up of soot but as I said, I've only done 300. Was the diagnostics at fault? Is there a leek somewhere whereby soot is building up on the DPF (hence the P3138 fault code? - whatever that means in layman's terms?!?!). Anyway car is booked in for Monday so fingers crossed.....