Problems with Seat Ibiza 1.4 16V, 63 kW (85 hp)1

Hello, I hope someone can help me here. The following problem, I drive above mentioned model now 1 year. Is an EU car. It was a new car, since last Monday my seat is now in a seat workshop only nobody finds the problem. I noticed that with the speed something is wrong, partly it did not go higher than 3000 and partly it is under driving just for a short time times on 0. I thought it was again a mad bit only that you could certainly out of the I brought my car to a general workshop, (they are also not a seat dealer but they are in my village and had still openly known owners well since I was always in the workshop with my car before), because it was already late in the evening. They could not help me and brought my car to a seat workshop. Yes, and there it is now. They also meant that they could not read the fault memory because it is an EU car??? Unfortunately I don’t know what I h h It is not possible that the car is standing for a good 2 weeks and no one can find anything? There is also a guarantee on the car. Maybe someone has helpful tips on how to proceed as I would like to have a car again. Thank you very much.