How to set dual sim to always use primary sim for outgoing calls?

I have 2 SIM cards in my iPhone max, and although I defined the primary SIM card to use for phone and mobile data in settings, when I make outgoing calls it selects the “latest used sim” for this. How can I change that?

it has cost me a lot of money this month because I did not realise I have to manually change this when I make a call and was not aware that I was using latest used sim instead of the one defined as primary, and therefore not using my local card but a foreign one instead.

please advise how to adjust this