Just had my rear Calipers replaced and now EBrake not grabbing securely?

Hello, if the technician replaced rear brake rotors or had them off the vehicle, then they should adjust the parking brake for you at no charge. If they only resurfaced rotors while on the car, or didn't resurface them at all, then they would not be responsible for this. Truth be told, though, frankly -- a repair technician should have checked the parking brake operation in conjunction with brake repairs anyway...so...i'd probably bring your case up to a service manager for discussion and hopeful resolution.