Hi, rear drum brakes tend to cause the sponge behavior.
Please do not do this yourself if you aren't DIY skilled.
They need to be adjusted. If you jack up your car by the rear wheel and you are able to rotate the wheel more than 1-2 turn by hand with medium force, then you need to adjust your rear brakes.
There is an adjuster wedge, which should be adjusted.
Please the rear wheel bearing needs to be removed, prior to getting the drum off.
Here is a picture of the adjuster wedge.
Place a flat end screwdriver on top of the wedge, support the brake shoe vertically at the bottom and carefully hit the adjuster wedge downward; this will make the brakes closer to the drum, limiting the brake pad travel.
Place the drum again and try to rotate. Adjust further if needed.
I made the mistake of buying one of these as well. I have never owned such an unreliable car, and spent more than the value of the car in repairs. In 6 months I had a new starter motor, front suspension arms, 4 new wheel bearings, a new water pump, an entire new exhaust and some new glow plugs. My car was low mileage and one owner from new as well.
After a year of shelling out money on a monthly basis, I got fed up and got rid. I am now driving a Ford Fiesta, which has so far been faultless. Needless to say, I will NEVER buy another VW!
I bought a 1997 Volvo 460 SI 1.8 with 40 thou to replace my unreliable 1999 diesel Polo saloon.
Easily the worst car I've ever owned. With all the faults mentioned I scrapped it as it was uneconomical to repair.
My 360 Volvo has been brilliant and reliable for the last three years and now over 120 thou and does 38 to 45 MPG and cost me 150 quid to buy. I spent the same again to give it a good service; tyres, pads, battery, etc then MOT and it is lovely to drive.