MTN CONTRACT

I have a contract with mtn which I pay every month on the 20th. For the last 2 months I have been paying on the 20th but I will just use my simcard for a week or 2 then my Sim card gets blocked reason being I'm owing which I don't understand how. I then called the call center and was assisted by Kim she said she sees my payment and will assist with unblocking the Sim which she did but also made a payment arrangement on my behalf without my consent or knowledge of the 17th and I was surprised to see my Sim blocked again saying I bridged and agreement which I am not aware of. I am not happy with Mtn at all more especially Kim who did things without my consent.