I agree with Bill, open a case with CMS, pay the Β£20 to do so (which also means you have control over when it's closed) and pay the calculated amount. If she refuses to give details, tell CMS that, and put the money you would be paying into a savings account - if she comes back at you for arrears, you'll have that money already to pay (in fact, I'd put it into premium bonds - you might just get lucky π )
Thank you all for your comments and I will go through maintenance. What do cms use to calculate the amount to pay? I have heard different ways like 3 months of latest pay slips and also the last full tax year. My job role has changed in recent months. Also, I get a car allowance and fuel allowance from my work and have heard they do and don't include it in the calculation. Advice welcome please. Many thanks.