Turn airplane mode on, wait 10 seconds, then turn it off. Ensure you have a strong cellular signal (not just Wi-Fi).
Unblocking a number does not "retroactively" send you the text messages they sent while they were blocked. Those messages are discarded by the network and will never appear on your phone. how to unblock blocked sms
Alternative Method via Phone App: Go to . The process to unblock is the same as above. Turn airplane mode on, wait 10 seconds, then turn it off