Maybe you amp is not working (sits behind C-pillar cover).
The rear window antenna and heater: The upper 3 lines on the glass are the AM radio antenna, the middle 8 are FM and defroster, and the bottom 8 are defrost
pic from Bill R
http://www.bimmernut.com/~billr/images/antenna.jpg
The amplifier and the rest is behind the C-pillars of the car. For the rear window heater on drivers side, but also some is on passenger side. Just remove the covers from the C-pillars.
The control of the defroster is done by the IHKA control unit. Maybe that is also not working.
So take a multimeter and the C-pillar covers, switch the defroster on and see if you get power there in and out.