Balance 20X VDSL Modem to use with "Deutsche Telekom"

Hi

We try to use a Balance 20x with VDSL module with a VDSL line of Deutsche Telekom in Germany.
Dispite the fact, that we use the correct VLAN (7), the correct VPI (1) and VCI (32) the modem is stuck in handshakes.
Does anyone have a suggestion what is wrong?

Greetings from Germany

Jan