Harassment for payment

This company harass me for payment from Finchoice that has handed me over after payment arrangement was made. After talking to a manager and forwarding proof of payment to another company that there is a standing arrangement with, they phone and send sms messages on a daily basis. Sometimes more than once. When asked to stop calling they either end the call, or they want to explain how things work. I pretty much do not care, I have an arrangement and I am paying.