hmm thank you munky261 for you instructions.
I tried it with macchanger

1. disconnect wlanhotspot
2. macchanger --r wlan0
3. connect
4. get new trial

this changes my mac. After changing I could not connect to my wlan any more. So I deactivated the wlan encryption for some minutes. It worked and I could achieve a new trial. But after reseting my device the mac changes back to it´s original and the trial does not work any more, but wlan works again even with decryption. Hm. btw changing the date does not work for me :>