Text messages and imessages marked as delivered yet not received since last update. I cannot make sense of the troubleshooting page, why does this complex machine not just work?.

I updated my iphone -again, and now my girlfriend (and who knows who else) is not reliably receiving messages. I try sending as iMessage and as SMS and have iMessage checked in my options and send as text message if iMessage doesn't work also checked. It was working fine, I updated, now it's patchy at best and although messages are marked as delivered they aren't and I don't know unless I phone the recipient up. Have tried restarting, resetting and digging through the trouble shooting pages... Apple products used to just work, now my phone is like a puzzle that I have to solve. I'm ditching apple in October when my contract is up but would like to send texts in the meantime, any ideas?