Unable to receive SMS/MMS while talking on the phone

My phone is Moto G5s plus.
Plan - My choice +2gb
Sim card - CDMA (due to coverage issues republic wireless have had replaced my GSM sim card with CDMA sim card)

i have recently noticed that while i am talking on the phone , i am unable to receive any SMS/MMS. I will receive all pending SMS once i hang up.
Recently while i was talking to the my bank representative , they sent a security code as SMS and i was not able receive the SMS/code until hung up the line.
While talking if swipe down the notification bar, i can see a republic wireless ‘arch’ and 'republic wireless" in RED color and a message saying “voice calls only”.

Could somebody tell me why i am not able to receive SMS/MMS while i am talking on the phone?

Thanks,
Mathew

I believe it’s because with CDMA/Sprint you lose the data connection while on a call. With Republic SMS and MMS messages are through the data connection.

If you were connected to WiFi during those calls the messages should’ve worked.

Yes you are right! I don’t have that issue when I am concerned to WiFi

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