Call again. Tell them you have had no luck. If you continue to get ignored, contact your congressperson's office and get the immigration liaison officer there to follow up for you.
It's been a while since I've posted here! Life's been crazy since arriving.
We arrived on May 10th 2015, I received my green card around July time but had problems with getting an SSN. It was the reverse for my wife. She got her SSN within 3 weeks without us having to do anything but her GC is yet to arrive today.
We checked USCIS a few times - always stuck on "in process", called a few times and eventually got told it was "stuck in Texas". Called again a month later and they told us they would start the process again. Finally today (a month since that last call) we checked USCIS and the status changed to "card produced". Fingers crossed we should receive it in the next couple of weeks.
Moral of the story, just keep chasing. To be honest, in comparison with the UK, these nuances have been dealt with much more efficiently here.