Might sound stupid but do you park up on slopes at all, as this may indicate low oil.
When on my drive at home it says low oil even though on the flat it's over half.
Check your oil ffs! Mine did this and now I have no car!
I did check it.. its fresh oil and completely full? like I said in the OP.
Did you fill it on your drive by any chance? Check it on the flat. Also find a specialist who can work out if your oil pump is pumping...
Could be a faulty oil presure sender (Had it on mine) need to get it checked properly tho as it might be telling the truth and you could end up with a shagged engine
Cheers, do you think the garage would have done this?