O2 contract cancellation

I recently moved to a new flat and I waited more than 1 month (paying) for the technician to come. After multiple missing appointments and different answers received by the O2 operators, the technical service claimed that it was not possible to install ADSL in the new apartment (just by phone call, without coming). They give me instruction how to cancel that contract in order to open a new one with a SIM card. I followed the indications and I gave back the router. I received the acknowledgment of both (included the e mail sent to cancel the old contract, otherwise it was not possible to open a new contract). Unfortunately the new connection was not so good and I canceled in the same way the contract within the 14 days as it is my right. Now I received a bill regarding the old contract. I asked informations to the shop and they cancel it another time for me last saturday. I am asking O2 to give me the money back for these months since I did not receive any service (O2 was not able to provide me with internet connection) and I followed the instruction you gave by phone to cancel the contract (If I am not wrong phone call are registered). Thank you for your help.