Telekom bill - enourmous amount (Munich)

Dear fellow expats.
i got a bill from telekom on my job phone around 7ooo euro for one month. I dodnt call, I just used the yahoo, facebook, and sometimes youtube.
They wrote on my bill that I entered on some porn sites - which i didnt used and i am not stupid to use on a company phone .
Anyway you got the idea. What can I do now? 7ooo euro for one month bill is ..........enourmous.
Please give me some guidance and ideas.
Thanks