Harra*****t

I would like to express the "harassments" I am receiving from this company. I pay my account on time, however, they phone me atleast five times a day regarding the next payment arrangement. And if I don't answer their calls, because I am at work, they send threatening text messages to say "they will pursue further legal action against me as I am not answering their calls". If someone is paying them on time, and the agreed amount, why do they keep on phoning me. In some instances I have paid them more than the required amount!