DPF serious issue and driving in limp mode

Dear Members, 

I seek advice, guidance with a hope to resolve the issue I have developed with my Audi A6 2.7 Avant (S Line 2010 Special Ed).  I have searched on various threads and read a lot about this; however cannot find anything similar to what I am experiencing.  Basically in a nut shell...

Before I start, the car has always been serviced by Audi regularly, last one was last year April 2018. I am based in South London.

DPF light came on and I had been driving the car for at most 2 weeks for short trips about 20 - 25 miles a day; however not long high speeds... just didn't get the time for a long drive. Knowing that I didn't have the time to go for a long drive, I decided to get the higher revs, I shall drive in Sports Mode so this may help a little. 

I had been driving around during the morning and in the afternoon upon a journey suddenly together with the DPF light, the Glow Plug coil light began to flash; I had never seen this before. Not long after, as I accelerated, suddenly I felt a huge loss of power and got really worried. As I gently pressed the throttle a little, I discovered that there was a bit of power, almost 5% and barely reached speeds of 20MPH unless I built up momentum. 

Unfortunately due to work and life pressures, I had to drive like this for a day and then spoke to a trusted local garage and gave my car to them.  They like to spend their time, investigate, look at options, cleaning the dpf, replacing it etc.  However, after connecting a variety of computer systems to the car, the garage was able to determine only a bit of info.  When trying to access the channels, they could not and tried other VAG systems and still could not.  

The conclusion is almost that even if the dpf is cleaned or replaced; if the VAG cannot get through to the correct channels and talk with each other; it is a defeated task.  So, is this a software issue, hardware, is there a password, has the dpf been damaged so much so that the channels have been blown?!  Do the pressure pipes need changing, does the oxygen sensor need assessing... so many questions and not even sure if they are the right questions.

Some info that may help:

P2463  Diesel Particulate Filter Soot Accumulation - Upper Limit Exceeded

P2002 Particulate Trap Bank 1 Efficiency below threshold: Implausible Signal

I think the garage may return the car as they have had it for 3 weeks and have not been able to get past this hurdle. They are honest and have tried their best; if there are any last few things you could suggest which they could try; I can ask them to.  Otherwise, what would you suggest please. 

Your advice and guidance would be much appreciated.