Engine Problem with Jetta 2010- Please HELP

[fatabass]

I have a Jetta 2010, 1.4, petrol. I recently noticed that its misfiring and burning oil. Had someone look at it and they think the issue is with one of the cylinders. I've been filling it with 5W30 semi-synthetic so far and has been driving well. However, last few days it has lost power, cannot drive more than 60 kmh and engine light keeps flashing. Would changing oil to a thicker higher viscosity oil help? Can I prolong the life of the engine by using a thicker oil?? Any suggestions on what to do? the power loss has been sudden and as soon as I switch on the car the engine light starts to flash and I get the "check the engine" message and also vibrates especially at idle.

I got a quote from a mechanic near Parramatta (west Sydney) for 3.5k for a rebuild, does anyone know if this is a fair price. (I dont have this money now and wont have for a couple of months). The car only has 95000km on it.

I am new to Australia and bought this car a few months ago, according to VW the previous owner knew about this issue but didnt tell me.

Any help would be appreciated.

Thanks