Engine won't turn off even with key removed

[Chalky84]

Right im brand new to this so here goes. Iv got an audi a6 2.0tdi saloon in black on a 58 plate. Problem is when I turn the key to off position the engine stays running also the dash symbol of the brakes with a lightening sign appears. I have to pull a fuse to kill the engine and place it back in time. Iv had it looked at and there is all sorts of codes being thrown up on the ecu so thinking that could be the culprit. Also possibly the convenience module unit coild be at fault.  Any info you folks could give would be much appreciated if any of yous have had similar probless. Cheers👍