With my Samsung S10e, after the latest software update G970FXXU3BSKO and security patch Dec 1 2019, I am unable to make Whatsapp call or any other voip apps when I don't have my WiFi.
Have you checked for app updates?
Could you provide me with your model code?
Was your device purchased in the US?
So from what it sounds like this is a compatibility issue with Android 10. With it just recently being released to the Samsung devices some applications won't be fully updated just yet.
I am facing the same Issue with my Note 10 Plus after recent Android 10 update, January 2020. (Unlocked Phone - Samsung USA)
Not only whatsapp calls but none of thr Voip calls are working. Is Samsung working on some kind of fix?