DSL contract termination

Dear O2,

I would like to terminate my DSL o2 contract. I have a plan that allow me to do so in 4 weeks, so I would like to do it by today.

Is that possible? What is the procedure? Last year I tried to terminate also my mobile contract and it did not work....

so I am wondering what is the quickest and safest way to do it now for the DSL (and only for that).

Cheers,

Laura !