@CrAcKeZ
To make it easier I will continue in a and b way,
a) look how our user community cooperate, investigating, looking for solutions,
We have found that in our case the ISP is deliberately disabled administrator account, for now without solution.
Try on the local forums find more info.
.Delboy was search and give you an example.
b) I understand your anger or frustration, VDSL routers are still rare and relatively expensive.
Switching device (Speedport) in Bridge mode for Internet connection and transferring routing job to another device solves your problem with the TR069 or remote management.
In this way you avoid remote access to your network (Lan) or remotely change your custom settings.
An investment in your router does not have to be expensive,
for example TL-WR841ND >
http://www.e-shop.gr/tp-link-tl-wr84...r-p-PER.612324
29.90 €
or small beast TL-WR1043ND >
http://www.e-shop.gr/tp-link-tl-wr10...r-p-PER.612438
59.90 €