How to cancel on-going DSL order?

Hello. I have ordered DSL from O2, but I was told yesterday that I cannot have a cabled connection into my apartment. I tried calling customer service, but they only have few people speaking english, and after 1 hour, the call got disconnected. I therefore wanted to know how to tell O2 that I want to cancel my order, and also how to return the router that I got.

Thanks.