Anyone who had problems enabling call forwarding?

I've set up my VoipBuster account: I can be called and call from that account. All seems to work fine. I've checked and I can call my mobile phone using this account.

Now I would like to forward this account's number to my mobile phone. So I dial *720611078xxx# and get a different dial tone to indicate my request is processed. Via the 2820Vn webinterface I get the information that it was configured succesfully.

But: it doesn't work correctly. When someone now dials my VoipBuster dial-in number, they get an 'incorrect number' error tone. I've tried playing with the settings, adding an international country code to the number and some other things, but I can't get it to work.

VoipBuster also has a PC software telephone program. From what I could see, you can enable call forwarding within that program, so I assume that the VoipBuster account itself supports call forwarding.

Latest firmware, v3.3.3. Any ideas how to get this working?

Thanks,
Matthijs