Paying CSA arrears but still they threaten bailiffs

Just been hit with liability order (scotland) says i have missed payments but have DOE in place and never missed payment since amount was agreed after lenghly arguments.

Spoke to them on phone and they are not backing down. My landlord says he will evict me because he does not want bailiffs at his door. I am already paying as much as i can, £61.oo per week for 1 child £46.00 for arrears of £21.500 which £19,500 are for my ex so why are csa chasing me for it?

They say i owe her it because she was not claiming benefits. Does council tax and housing benefit not count because i know she was claiming these things?

Any help would be great people

thank you
alex miller