Mk2 Recurring DPF Issue

Hi there. New to the forum and looking for some help/ideas please. Firstly I'm really sorry if I'm using confusing terms as my car knowledge only goes so far, so will probably say some things that sound pretty dumb to someone who understands cars a lot more than I do!

I've got a 2008 1.6 TDCi. It has an intermittent issue with the DPF (or something causing this) which triggers an engine malfunction and goes into limp mode. I don't have error codes as my mechanic was taking care of it, but he's ceased trading recently so I'm now having to start afresh with a new garage. Basically it seems that the diagnostic is saying that the DPF is full/clogged and can't initiate a regen by itself. I've had a few electronic regens which seemed to have cleared the problem. We put it down to a lot of short/interrupted journeys (got some really crappy roads round here - roundabouts every couple of miles even on the major routes).

The new garage dealt with the last malfunction, which was a few weeks ago. They found that the DPF actually only had 6g (I think) of soot so they were really confused why it had triggered the malfunction. They delved a bit deeper and found that the exhaust sensor wasn't working properly, which was probably what was causing the malfunction. Seems that every time my previous garage had reset the DPF, it may have made the issue worse as the sensor's 'zero' then got a bit higher each time. (Not explained that well but hopefully you get what I mean). New garage was pretty sure that should have sorted it.

Anyway, it's gone again. Car's going in on Thursday but as above I'm doubtful that the DPF is actually full/clogged as it was only sorted 10 weeks ago and I've not driven her a massive amount (although I have done a few longer, high-speed journeys). 

Has anyone else had similar to this, and can you give me any ideas on what it was? I'm really not in a position to get a new car but this is getting a real problem as she's in limp mode so frequently and I've lost confidence in driving her very far.

Thanks so much, Jess