CGT Visibility - Calculations and £ Due

We sold a property last year and completed CGT forms and submitted it (albeit 30 days late - an error on my part - so expect a fine!). My wife and are are not UK residents (I have a UK passport and my wife an EU passport). We had a 50:50 share of the property. We complete a normal tax return each year and do not earn enough from 2 residential properties to incur tax. Mail to Hungary (our tax residence) is poor and intermittent - however, we receive some letters. I am looking at my personal tax number through the Gateway and it says there is nothing owed from either my return or anything else. I called HMRC and they said both my wife and I owe monies for CGT - can anyone advise where I can see this online? My wife has no Gateway / NI number as a non-resident and is not entitled to either so only receives paper correspondence. Is there an area that shows actual calculations used by HMRC as the CGT charge vary between my wife and myself. My charge for CGT is double hers - we reported exactly the same figures to HMRC to the best of my understanding - our income is equal to each other. Cannot understand why there would be variance. can anyone suggest the best route forward? Thank you

Hi,
A calculation will have been issued to show the tax due, it is likely you will need to contact us direct to discuss this further.
You can do this via webchat - Self Assessment tax returns How to get help - select digital help
Thank you.