My iphone 5 is showing an unread message although there's no unread message?

So earlier today I accidentally deleted the conversation between my boyfriend and I on my iphone 5. Since then I started having problems. I would read his message and respond, and then I would pull down the task manager and it would give me all the texts he sent me, and implying they were unread. Somehow the conversation was deleted again (99% sure it was not me this time) but not my phone is telling me i have 11 unread messages.

I have tried resetting it, many times.
I have tried the sleep button and the home button reset.
I have tried updating the software.
And because the conversation was deleted, I can't go back and read them because they are gone!
Nothing is working.

Do a complete shutdown and reboot it.

Manually delete the messages by tapping the "X" beside the notification.

Also, another way to reset is by pressing and holding the sleep/wake button and the home button at the same time until the device reboots.