Contacts continually disappear

My contacts continually just disappear. There is no common factor as to when this occurs. I will just see that all my texts are from numbers instead of the contact that sent them. My contacts are on the SIM and I have turned off iCloud contacts. I even deleted the iCloud account, Imported SIM Contacts, restarted the phone and still nothing. I have done this over 20 times in the past 24 hours and still no contacts.