No resolution to my query and no one has made an effort to resolve

No resolution to my query and no one has made an effort to resolve. Instead I get bombarded by calls to pay an account which I did not agree to open an account, a consultant admitted to their system automatically moving me to a month to month contract and I refuse to pay it as I finished my 36month contract and didn’t request to continue with the service. They also did not notify me that the contract is end and that I have an option to take out a month to month contract.