Dependant visa extension payment mismatch issue

[Markus2]

Hello,

My wife is applying as a PBS dependant.

I received ILR through skilled worker route and she does not qualify yet so she needs to apply for 3 year extension.

As I received ILR through Skilled worker route, I had to put end date of COS as a random date in order to get correct IHS fee.

I filled out application today (14.1.2025.) and set COS expiry date as 13.1.2028. (three years minus 1 day).

I got IHS payment calculated at 3,105gbp for three years so I paid that.

I then got to application payment screen and got amount of 1,636gbp instead of 827gbp.

According to official website, this payment amount is classified as "more than 3 years" instead of 3 years.

I am really confused as I already paid 3 years IHS.

What should I do now?

Does anyone know why this happened and what should I do to avoid it?