UNECCESSARY HARRASMENT FROM SCS

I have a payment agreement with Sustainable Collection Services to pay off my Direct Axis account for monthly amount of R50 which was accepted in writing (attached copy of email) and yet i am still being CONSTANTLY HARASSED by SCS month after month threatening me with sms's informing me they are going to take "further legal action" (copy of sms screenshot attached). THIS IS UNACCEPTABLE AND TOTALLY UNCALLED FOR when i already have made payment arrangements. I am sick and tired of receiving these threatening sms's month after month and don't tell me it's an "automated sms" that gets sent out. BULL****!