So, my partner's ex wife spent the better part of 2 years hiding any money she received and claiming we hadn't paid her anything at all.
During this period we sent her approximately £16,000.
She opened a case with the CMS. We thought this would be a good thing because she surely can't lie to a government organisation and get away with it... but we were wrong. The CMS is set up to benefit receiving parents. If you are the paying parents, don't think you will get treated fairly. This isn't due to any malice; the CMS is grossly one sided out of necessity - they deal with thousands of parents that can't or won't pay and they have to be primed to handle this.
At times the CMS were claiming we owed up to £12,000 when in fact we had made several overpayments. They were useless with bank statements as evidence etc. They didn't refuse them, they just didn't seem to know how to handle a situation where the receiving parent says one thing and the paying parent demonstrates another. You get no dedicated case worker - just passed around a very over stretched and under funded organisation.
Sorry, this is all relevant...
Parallel to this was another issue of "variation". My partner is self employed and the ex wife filed a variation to have the CMS investigate him for money she thought he was hiding. He wasn't hiding any money but we are both reasonably "high earners" and she was cross that my income wasn't taken into account too.
Eventually it went to court and they found "in favour" of my partner. That's to say, that they accepted we owed no arrears and that we were paying the correct amount. This all took about 3 years to resolve but we finally have this in writing!
In the meantime, we have been stuck using a "service" they call "Collect and Pay". This service takes an extra 20% from the paying parent and is how the CMS fund themselves. For us, this amounts to thousands of extra pounds per year.
A receiving parent can request that a paying parent is moved to Collect and Pay just by pretending to not have received one payment. You are then stuck on this service for a minimum of 6 months.
That is to say, the can be weaponised against you and unless you have a fantastic relationship with his ex partner, stay away from the CMS.
To summarise:
CMS don't handle the paying parent with the same care that they handle the receiving parent. Beware.
CMS could end up costing you an extra 20% per annum and the children will not benefit from this. Beware!!
CMS will ask for evidence of everything you try to claim - such as mileage. If ex wife disputes this, you could find yourself going around in circles for years.
If you are considering contacting the CMS so that you can have this travel amount legitimised, but you are currently in a private agreement with his ex, I would think twice. Especially if you have strained relations with her. If she feels in any way "wounded" by a reduction in income and decides to "retaliate", everyone will suffer - especially the children.