Why give up so quickly? Use the social media support channels, tell them "self installation failed" and they will send a technician for free to set you up. If he finds out that in fact no cable connection is possible, VF will cancel the contract (though they already sent you the hardware, so theoretical cable should be possible). I would prefer VF cable over DSL.
If you ordered online, you have 14 days after receiving the hardware/documents to withdraw the order (make sure to really do a "Widerruf", not a "Kündigung", and send it to the correct contact - all that should be stated in the documents they sent you with the hardware). If you ordered in a store, there is no such right and you are stuck with the contract for 24 months (again, if cable is possible).
