Sending my account for debt collection

I have made an arrangement with african bank about my loan instalments of wich they have been deducting money from my bank every month. Last deduction was on the 2016-03-01 then I got a suprise visit from a guy that works for Blake and associates telling me that he was sent by African bank to let me know about the status of my account not realizing that the papers he had showed my last agreed payment. He then adviced me to stop the payments with african bank and pay them instead. Why did African bank send my details to them because i am paying the agreed arranged instalments. I want clarity on this. I refused to sign the documents he had and also I disliked the suprise visit. Why didnt they call me before coming to my home. He also told that if i do not sign the account will be sent for garnishee. The aproach was unprofessional