Do you have a limit set by your carrier in terms of number of SMS/MMS? It could also be that you've only allowed 4G in your cellular settings, and SMS/MMS can't go through.
In Settings, under Data, check 3G/2G along with 4G. Also check if there's your carrier name under Calls and SMS. If not, tap on the SMS line, and check the line for your carrier.
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