Mitsubishi Lancer 2008: Faulty ABS

My son has a 2008 Mitsubishi Lancer with ABS brakes that failed. He got a replacement at the wreckers and had them installed and they work fine, but the ABS dash light still stays on. He took it to the dealer at Capalaba and they told him they could fix it while he was there for $25, but when he came back they said it didn't work. They then did another job for $25, which had the same result. They then said they could do another job, which would take 2 hours for another $250. In the end after sitting with his 2-year-old son for three hours and spending $300, which he had to pay as they had his keys, the car still has the dash light on. Any information to assist would be greatly appreciated.