I had a similar problem, that I did not receive any (or many) invitations, even through my balance was something like $20. Then when they took the 75% (or whatever it is), that left me with some odd amount like $7.56 - but still no more e-mails!

So what I did was sign up using one of my other addys! Now the emails come through fine, and that account has something like $115.00 in it! (But still nothing new on the old account. )