After getting my LCD screen repaired, my firmware file is suddenly not compatible

The pixels in my screen were dying so first I took it to the apple store where they told me that either they could do an expensive repair or get a new ipod. So i went to a local phone repair store so they could fix it cheaper than the apple store. When I got it back, there was nothing on my ipod.. so i figured they had just reset it and I would just plug it in and I could get all my music back on. But when I plugged it in, an error message that said "itunes has detected an ipod that appears to be corrupted." and told me it needed to be restored. So when I tried to restore it, another error message came up saying that it couldnt be restored because my firmware file is not compatible. I also noticed that the back of the ipod says it's a 160gb model when my ipod is actually the 120gb model. I was confused so I called the store and they told me they had to replace some parts of mine with another ipod's parts for some reason. My ipod also has a new serial number.. So I took it to the genius bar and they reset it and it seemed to work fine but when I got home and tried to plug it in, i got the same error messages. So I called apple and someone walked me through TONS of solutions, but all of them to no avail because the problem is the hardware on my ipod. Does anyone know what might be wrong with it? If it's unfixable, i believe a certain phone repair shop owes me another ipod.