How can I buy ONLY DSL Router

Hi. I signed a contract with O2 DSL on October 7 and said that I only need to install a router because Technica activated the Internet on October 23. But I did not speak German well, so I ordered without a router. Therefore, I bought a cable with the fritz box 4040 in Saturn on the 24th and installed it. The router and the smartphone need to be connected, but the router cannot connect to the Internet. I haven't been able to use the Internet for a month since the date of the announcement. Already, contracts have begun and money is being withdrawn, and the Internet has never been used. Even if you ask Live Chat, you can just say things like a parrot without giving a clear answer. I post here because I am really angry and think O2 is too incompetent to ask consumers directly. If I buy a router separately, I want to know whether the connection is not working, and if I have to buy the router at O2, how to buy it.