Moved the SIM card from an iPhone 6 to a Samsung Galaxy S20, cannot receive texts from iPhone users

A friend had an iPhone 6 and received a newer Samsung Galaxy S20 phone. He moved the SIM card from the iPhone to the Samsung phone. He had trouble receiving text messages. He removed the SIM card and put it back in the iPhone and followed instructions to delete all messages on the SIM card. Now, in the Samsung phone, it receives text messages fine from most people, but certain iPhone user texts are not received.