They have dislodged an ABS sensor and not done the job properly.
They should have found this on the test drive and fixed it without you knowing.
Going too cheap gives issues.
Use a decent garage not a bunch of cowboys.
The fact that the ABS light came on after new parts were fitted suggests something has been disturbed or not refitted correctly or damaged in the process. If the fault was not there before your visit then it is the responsibility of the garage to correct it at no cost to yourself. Stand your ground and insist they correct it, accept no argument that you should pay or contribute to the costs. An ABS light is an MOT fail so technically your vehicle is not roadworthy.
What they say is plausible - it is possible they accidentally disconnected a sensor when working on the brakes, and didn't reconnect it until you went back because the light came on.
Until they clear the fault from the system, you won't know if they have fixed it.
If they have, the light will stay out.
If they haven't, it will come on again within a mile or so.
They probably haven't fitted the sensor properly and will now try to charge you for fixing something that was their fault.
I took my car to the garage to get brake pads and discs fitted, when i was leaving i noticed the abs light was on so took it back, they then checked the car and said the plug or cable had came loose and they had refitted it but the light is still on. They have said i need to get the light took off and i have to take back and they will put it on the computer to fix, is this true or have they done something to the abs? I dont want to chance driving long distances if the abs is faulty and am on a tight budget so dont want to shell out if what the garage are saying is true?