No internet when on a call

Hello!

I am using a iPhone 12 Max Pro and two SIM cards - one nano on Three and a eSIM on Vodafone.

Everytime I receive a phone call I seem to lose all internet access - data switching is on so either network can provide the access however I always get a no internet message.

Having internet access while on a call is pretty vital for my business.

I’ve been through all the settings and cannot find anything - am I missing something?

Just to clarify - the Three SIM has unlimited data and the Vodafone eSIM has 50GB.