Electrical issue on octavia VRS 2007

I have a serious issue with the car and can't work out what the problem is.

Had the head unit replaced with a after market one and a few months later I noticed my demister wasn't working. Checked the fuse and noticed that it had almost melted.

When I took it out my engine management light and glow plug light came on straight away.

Had it diagnosed and came up with a MAF fault which I replaced but still didn't put the lights out. I have since changed it 3 more times without any success and now have other warning lights come on which I can't clear.

Run another scan and the garage said I have a grounding fault.

Took the car to a auto electrician this morning and he said I have a problem with my Canbus gateway.

Please help as my MOT is due next week.