iPhone Xs MAX dual-sim issue

I have had the Xs MAX for about 1 week now and noticed there is an issue with the dual sim support of the phone. I have the Chinese version (model A2104) so i can insert 2 physical nano sims.

The issue with the sim card that does on top is:

1. It takes long to get signal

2. takes long before a ring is heard while calling someone

3. when someone is calling me, it tells them that " the person you are calling is not available"

4. overall slow when accessing something that has to with the carrier.

so I decided let me use the bottom sim slot.

The bottom one fixed all those issues but then had another issue:

when i try to buy bundles (here in Kenya (safaricom) we dial *544#) and dial the code, as expected it opens up the menu for buying bundles and types the number 7 that would usually take me the next menu to continue the process of buying internet bundles BUT unfortunately, the menu disappears and doesn't come back.

This is a very big issue for me as currently i cant really buy any bundles or use other services available through the carriers menus.

I hope someone from apple can reach out and tell me how to fix the issue.