I also used the family pack.
First, note that these SKUs have not been sold (by MS) in quite a long time. They do still appear in online stores, though, and they are quite a good deal.
Having said that, I always have to call MS and talk to someone to complete my activation. I have activated one key on my desktop and a second on my partner's desktop. I have kept the third key aside for a laptop, but the two i've bought have had Win 7 preinstalled .. so the third key remains.
I've never had MS tell me to pay a fee, though, and $50 is not something I've ever seen in their fee structure. Are you talking to them directly? On the phone?