Whch modem/router are you using? Is the DSL light going out or blinking at that situation?

Blinking. FritzBox 7490 is the modem.

@juliano7s can you please post this screenshots from the Fritzbox for us? (Übersicht and DSL) 

Gladly.

@juliano7s please make a technical ticket at the o2 dsl Hotline. 0800 52 51 37 8 (Call with mobile please)
Did you have a german speaking friend nearby? Recommend the Resyc. You must have normally a sync with 100Mbit with your line.

Hi @juliano7s,

thanks a lot for your patience.

Did you already reach our technical DSL department by calling the hotline as @Joe Doe suggested?

I hope you were already successful.

Loving greetings,

Tobias