Sanyo MM-8300

help!!! when i recieve text messages the number of the person who sent it to me shows up but not their name. and i even have them in my phonebook too. and when i send them a text message and go to my sent folder their name shows up..only when they text me it just shows their number an its pissing me off because i dont know everyones number..only their name.... does anyone know how to fix it????????