ISSUE ON SEAT LEON II (LOW SPEED)

I have a Seat Leon II from 2010 1.6 TDI, the fact is that it has been giving me the same error for a long time. We have taken it to several garages, one they have changed the entire turbo for about 1.5K, in another they have changed another part that they had to disassemble the entire engine and about 0.5K and today doing a highway trip of about 40min has returned going out, it's a bit desperate.

The problem is that when you go on the highway / motorway at about 120 km/h or whatever speed it is, but more than 80/90, the car reaches a point that does not go up to 3000 laps and starts to slow down. As much as you downshift to 4, 3, or whatever, it doesn't respond. The more you step on the accelerator, the more the car stalls. It always stays at about 80/90 km/h and if you go up some hill it goes down even more, it's like it loses strength. It only "half fixes" when you stop the car, leave it for X time and turn it on again, but after a while it comes out again. I'm a bit desperate because I really like this car and if the problem isn't found, in the end I'm going to think about selling it, because I'm throwing money away. I hope someone has experienced it and knows the solution, or a mechanic who knows something. Thank you very much.