Inconsistent and bad customer service

I sent an email on the 6th,7th and 15th of February confirmation of the payment arrangement and advise to deduct on the 26th of each month for the amount of R265 yet this people is sending me threatening emails and call after call when I agreed to the payment plan they sent me! Why on earth are they sending me SMSes and emails threatening to pay I will take them further if this keeps going as I have confirmed via email regarding the payment plan!!!!