I'm going to say this one more time. Real slow.
The. Financial. Investigation. Unit. Are. The. Powers. That. Be.
My ex pretended he didn't live in the country.
CMS chimps went "dunno what to tell you really, we have to go on what he says"
HMRC went "dunno what to say really, he isn't filling in any tax returns"
I shouted at both agencies til I was blue in the face that I could send them a picture of him getting into his very English car, outside his very English house, in England, every day. But apparently that wasn't evidence.
I called my MP, as you can imagine, fuming.
She made one call. The FIU were involved. They froze his accounts. Went through every bit of income he had diverted. I now have a current CMS payment plan of £734 a month and arrears of £30k+ generated purely from the involvement of the FIU.
HMRC are still scratching their arses as to why he hasn't filled in a tax return.
OP, if you are still going to sit playing "baffled" what to do when so many have spelled out exactly what your options are, then there's little point of this thread.