Hi everyone,
First of all a special thanks to @silver1011, @skomaz and @2010OctaviaScout,
You guys saved me alot of money as it appeared to be the hose that caused the issue.
The locking mechanism / connection mechanism for the hose was a strange one. I had to reattach it like 3-4 times for it to attach properly, and so I can actually understand why my mechanic though it was attached but then popped off again. So after a few attempts I was able to attach it properly and the car ran perfectly fine again. No glow plug light. Engine light was still there so I took it back to my mechanic and he cleared fault codes. Haven't had a single light afterwards!
So again thank you so much all of you - really saved my weekend.
All the best!