NOS unsubscribe, help requested (Lisbon)

hello all,
As new comer in wonderful Lisboa (Graça) on July Protected content , I subscribed "4x play" contract with NOS. Everything went well until March Protected content we decided to inform NOS about our move to Alfama. But since they have no cable network in the area we live now, NOS suggested satellite connection, no way too because local authorities do not accept aerial on our building. We sent registered letter to NOS explaining we want to finish the deal because of their inability to provide Internet, and ask them to pick up their material back. After 4 months and more than 20 unsuccessful phone calls, NOS never answer to our request and continue to send monthly ninvoice we refuse to pay. They pay regularly calls sometime asking if we are satisfied with contract, sometime asking wether family members or friends could continue the contract in our place, or sometime telling we are engaged in a 2 years contract and therefore have to pay Protected content as penalty.
Did some of you met this kind of situation which look like a no ending story.? I really don't know what is the right attitude towards these people. Any help or advice will be welcome!