iMessage “activation unsuccessful”

Since I first got the new iPhone 12, my “send & receive iMessages” has been set to just my Apple ID and I have never been able to send messages as a normal SMS text message, only iMessages using my Apple ID. I tried to add my phone number to send and receive messages from but it would show the loading symbol for hours and would just never work. I turned off and on my iMessages again but now whenever I go to add my phone number to it a error pops up saying “An error occurred during activation”. I have the “send as SMS when iMessage is unavailable” toggle on and I thought that might have helped the situation but still no luck, I keep getting the error pop up. Is there any way I can fix this problem?