06 VW Jetta antenna

I have a customer with a 06 VW Jetta. This Puppy has the antenna now built into the rear window. I see the antenna box where the antennas plug into and seem to be fine. I get fm signal fine, but for the am i get nothing. All we did was tint the rear window and well this problem occured. So we stripped the window and same problem. Next we took it to the dealer and well you know dealers and 12 Volt Shops don't get along. They are saying that we cut the lines on it, but when you tint you cut from the outside and lay from the inside. So can anyone help me out or have had this problem before.

try to unplug the factory antenna and just plug in an amplified antenna in the radio sometimes it works fro am stations but thats about all i can think of if the antenna was not cut or removed