Harassment of Call Centre Agents

I made a payment arrangement with the company in the beginning of this year to pay off the account. I have in the last three months increased my payment amount. It is very annoying to received up to 6 phone calls a day in regard to them telling you that you need to pay by the first of the month. I have not reneged on my payment arrangement once and have no intention on doing so. However, despite advising them on numerous occasions that they can contact if I don't pay they still bug me religiously every month for three days. It really gets my ire up and I find the attitude of the agents shocking. I have since downloaded an app and I will block each and every single call from that company. they have my email address and are welcome to communicate on that level as it gives me a trail of evidence should I required same. Remarkably I have sent them an email to ********** and ********** and the response back is they would get back to me in 30 Days...................... really!!!!!!! All I want is for them to stop phoning me at work and on my cell.