i am missing text messages sent to me, despite their being shown as delivered,
i have received messages from the senders in the past, and have just received another one from one sender. there seems to have been a period when Verizon did not deliver.
despite both the sender and me being on iOS/iphone5s, when the sender tries to text me they are told it must be sent as a text message, not Apple's iMessage.
how do i troubleshoot the issue?