Contaminated Diesel in my Diesel engine

Hi I’m new to this forum

i need help PLS

I have a Audi A7 2015 auto Diesel mileage 15k

had diesel drum in garden for last few months so decided to put it in car never drove it that night

nxt day few hours after driving it, it started to stall etc and wouldn’t turn over

fuel guys have come out and took fuel out etc,and still same problem  so today 30/07/2019 I got the fuel filter changed and primed it with diesel

car starts just about maximum for 5-7 seconds and clonks off or if I rev it, it clonks of quicker 

changed fuel filter on the advice of AA 

now I don’t know what to do any help will be appreciated 

****( the fuel I had put in was a drum just over half way full and was shell diesel that I had in a Clean drum sitting in the garden for last 5-6 months that diesel seen it all the temperature going minus zero few months ago and very hot in the last few weeks hence it getting contaminated as it was not stored correctly)****