Can't communicate with Engine Control Module

My 2013 Volt couldn't start, when I turn on, the front panel initializing took a minute then it appear with 6 vehicle messages: Service Brake Assist, Service StabiliTrak, Fuel Level Low, Service Power Steering, Ice Possible. Drive with Care and Service Theft Deterrent System. I had to tow the car to the dealer. First they charged me $286 to replace the battery, then they said that the car couldn't communicate with Engine Control Module (ECM) and they would charge $585 just access to ECM to find out what wrong and would quote to see how much to fix. I think it's rip off. The reason my car was lock out because I brought it to the a garage shop and they hook up an aftermarket device to run the diagnostic because of the headlight and the fuse burned. I'm having a headache with this car. Should I bring the car back to the dealer because they're the one place that can fix this problem. And I don't think it's going to be cheap. Any opinion would be much appreciate. Owning an Electric is not as fun as I thought it should be.