Complaint about contract Cancellation

I am having a terrible experience with NOS customer support. It’s been 4 months I am trying to cancel a contracT. I had endless calls since March, and yesterday they tell me that in one of the calls I renewed the contract! How ?!! Why would I renew a contract when I returned the router and all the items related to NOS?? They keep charging us invoices for a service we don’t get. This is really very annoying, I have made complaints and asked for help many times and NOBODY is being helpful on this matter! Every single time I talked to customer support I get transferred from one person to another, at the end I talk to one person and I explain the situation, and the answer is we call you back. 

We have signed all the documents that we want to cancel the service, we returned all the items. Just simply cancel the contract!! what is your problem!!