Posting everything in an open forum isn’t going to help your case, for what it’s worth and repeating myself, dont get hung up on the detail - if VW says it was low oil level that caused the failure and you had only driven it 2 miles from the repairer, then ask them to put it in writing and go and see the garage that did the repair and ask them what they propose to do about it - oh and dont tell anyone that you checked the oil after you left the garage.
If the subject of remap comes up then presumably they knew this before they started the repair and as such they must warrant their workmanship unless they told you otherwise when they found out it was remapped.
You might also consider that it might be better to stop speculating and keep to the facts around the failure i.e. the turbo failed and you paid a garage to fix it and it lasted 2 miles and the manufacturers agent says the low oil level caused the 2nd failure.
Apologies if this sounds like a rant, it isn’t as it really doesn’t matter to me but causation engineering is what I have done for the last 20 years and if I had to bet what the primary cause of failure was I would put my money on workmanship. I think you are probably being treated harshly by the repairer but you are not helping yourself by further complicating an already complex issue with ongoing speculation.
When dealing with these issues, start with what you can see and go from there, don't get hung up on history, rumour or speculation - just deal with the facts in front of you because everything else just confuses the issue.