Tikona — termination of internet service - legal notice - mental harassment

I have terminated Tikona Services few months back and informed them about it. This was done since I switched to a better service provider. I started receiving numerous calls from them which were answered. They also kept sending me SMS regarding payment. Since I was not using their services and informed them about I did not pay. Moreso they confirmed about removing my services but kept sending SMS. Today some Legal entity called and told me about filing a complaint for payments not done. This is mental harrasment from Tikona service creating deep disturbances for nuisance post breaking business releations with Tikona. Please help.