Refusal of fee reversal on fee that was not disclosed

I was charged a 9.99 shipping fee for a router, that a day after install I had to return. The technician who came refused to help me. He told me he works for Telekom not o2 and just left. I called multiple times and no one could send one signal to reset the router to clear the old occupants information which was activated due to the line being active when I prepared the router for the tech install. I bought my own router, due to the lack of knowledge and help with tech support, and mailed back the router to o2. I’ve only asked the 9.99 fee be reversed because it was not disclosed when I physically signed this contract, also on the contract I signed there is nothing indicating any fees for shipping. I’ve been hung up on by two reps, told by another I have to talk to the store, had the store tell me they can’t understand me and help me, because my spoken German isn’t good. This is just a horrible customer service experience.