O3 fuel pump problems

Hi all! This is my first post on this website so please be gentle.

I have a problem on my Octavia 3 2.0 TDI DSG CKFC (2013>>) and i am not able to figure it out.

So, I'll start with a little history of my problem:

When i first bought the car, the fuel gauge said that i had 1/2 of fuel, but suddenly the car died, and after investigations i found out that i had no fuel. I blamed the fuel sending unit. 

I've gone to a dealership and told them my problem and asked if i can change only the fuel sending unit. They told me that i can't, and i had to replace the fuel pump. (Wrong, the fuel sending unit can be replaced, but no one told me the code for the part. idk why)

After that i pulled out the fuel pump, cleaned it, measured it with a impedance meter to see if the sending unit works. It did. I put it all back together and the fuel gauge seemed to work. But surprise, instead of going down, the needle went up while i drove.

So, i've bought a new fuel pump with a sending unit from a scrap yard. I've asked for the code from my fuel pump but they gave me the equivalent from the Golf MK7 1.6 TDI. Anyway, after i tested and installed it, the fuel gauge worked, but i was unable to start the car (my thought is that the fuel pump for 1.6 TDI, cannot make enough pressure for a 2.0 TDI - i might be wrong)

Running out of options, i took the fuel sending unit from the new pomp and mounted it to my fuel pomp because my sending unit was dead.

So, now i have the next problem:

The car runs, the fuel gauge seems to move BUT i have the following error : "Error: fuel tank system. Workshop!"

Searching the error with VCDS i found an error that sounded like this: "Covering for fuel level indicator sensor 1, high resistance".

I'm out of ideas on how to calibrate or pair the new sender unit with the car. 

Any help is appreciated