How do I complain and who do I talk to?

I have been paying the csa prior to and since i left my old job and started a new one. OR SO I THORT. I have just called them back as they left a message.They have just told me that they have not received any payments for three months and that they have it set-up to come out of my wages.

I have tried to pay them since the payment was set-up. they have inbbarased me at my place of work to the point i don’t want to work there no more. They only started to get in tutch last week and i have been buzzy at work. how do i complain and who to