CSA gone to my employer even before the deadline for me to return documents has passed

I am happy to give further details if required. But to keep it as short as I can;

I was contacted on Friday 2nd March by the CSA to give details on my earnings.

I have never been married to the women in question and nor am I on the birth certificate.

I posted the form back on 7th March denying parenthood. Proof of postage and photocopies retained for proof.

However the CSA has already gone directly to my employer (letter sent on the 6th) demanding my salary information.

How can they contact my employee even before the expiry date has passed? Surely this is a blatant breach of process?