Not receiving all sms or mms message, puretalkusa

Hello we have one iPhone 11 and 4 SE gen 2 on our puretalk plan. We often do not receive messages especially when it is a group message. Sometimes one member will receive a message and the others won’t. Sometimes my Apple Watch will receive a message and my phone won’t. This only started when we changed from AT&T to PureTalkUSA.

1. we have mms and group message turned on.
2. we have contacted provider multiple times, each time they reset carrier settings or reassign/reset the sim. we follow directions, turn phone off and on. Turn wifi off for a time and on again.
3. problem continues. Is this IOS issue? We are current with 14.4.1
4. any help?