Termination of Contract

Dear Customer Service,

I am an O2 Blue All-In L customer. On 17/11/2016 my contract will expire and I would like to cancel it because I do not need it anymore. I run the procedure online and it said I had to call a certain number (040-51900 66 58) in order for the cancellation to be effective. I tried to call the number and the customer representative said she would have sent me some documents which I never received. Could I please get this form or can you advise how to terminate my contract in another way?

Also, I would like to know what's the earliest date I can terminate it.

Many Thanks

Francesco