macbook suddenly sending all messages as SMS not iMessage!!

Long story short - I got a new SIM card for a new phone line (but didn't have my other iphone for it unlocked yet). The customer service rep recommended that I swap the new SIM into the current device I had to make sure the number had been activated properly (big mistake!! and pretty sure the cause of all this). She promised me it wouldn't mess anything up but now suddenly my macbook & iphone have been inconsistently sending SMS messages to iphone users. In fact, I can't send iMessages at all from my macbook anymore! The only way it works on my iPhone is if the apple user responds back to me with iMessage it usually will convert my messages there after to iMessage. However this is NOT the case for my macbook. The iMessages fail to send from my mac and they end up having to send as SMS.

So far I have tried contacting T-Mobile tech support who then transferred me to Apple (no one could help).

Just noticed that I am able to send iMessage from my macbook to a very few select apple users when in the past there was no issue

I have:

-reset iPhone network settings

-factory reset my iPhone

-disabled iMessage in iPhone settings & turned off for several minutes before turning back on to re-enable iMessage

-signed out of messages in macbook & rebooted after several minutes

-toggled between having messages send & receive from my Apple ID & phone number for both devices

-enabled messages in iCloud