2004 Renault Clio Brakes catching on something

Brakes problem
2004 Renault Clio

Whilst reversing I pressed the brake pedal to find it wouldn't push down fully, seemed to be catching on something. Then, with a 'clunk' the pedal when down fully but the ABS warning light came on. I took the car in to the dealership and it was linked up to the computer, the fault was the cv boot which needed to be replaced as it was blocking the sensor.

Got that fixed, ABS light went off, but 2 months later whilst reversing the same feeling of the brake pedal being stuck happened again. Same 'clunk' then ABS light back on. Took back to garage and this time they said its the gaitor clip thats come off, paid to get that put back on but its not fixed the problem. The ABS light is still on and the pedal is still sometimes sticking.

Any ideas what it could be. I'm fed up of paying to have it looked at, paying to have it fixed. I don't trust the mechanics in either of my two local garages and now they want to charge me again to hook it back up to the computer to find the problem which so far they have failed to fix.