make sure that you have the Area Code in the Contact List.
lots of folks omit the Area Code and assume that just the 7 digit number will be "good enough".
not so with cellphones, they switch towers and areas like the plague... the Area Code is a requirement for making phone calls and SMS go where they should.
Also, very carefully, check your Contact List for hidden dupes... same name, but a different number?
Make a new contact with the same exact name spelling, and it should come up showing you that is a dupe for the one you already have.... if it comes up with the same name, but a different number..... trouble can happen.
Also, make a new contact and enter the correct number first, and leave the name blank, that should pop up the correct name you want... if it don't you have a dupe number, with a different name on it.