Of course warrantee is between you and the seller. I do not have anything to do with fastlane so I can't tell you their policy.
Brakes are a perishable commodity and situations like yours arise for all installers. Mostly the discs are exchanged, some shops cut the discs to true them on the car. You need to have numbers for the problem. How much are they out and is there runout in the flange?
Bosch Master, ASE Master, L1
33 years MB technician