How do I stop my blackberry from automatically erasing contacts in my address book?

From time to time, I go to look up a contact and that person has mysteriously been erased from my contact list. Blackberry support (which is a joke, worst I've ever seen) wants to charge me $50 just to talk with them. I know other people that have experienced the same problem with contacts just disappearing. One time, almost have of my list disappeared including my parents' cells. Please somebody help! Blackberry will not...

it could be a couple of different things. 1st do you have filters applied to youre contact list? go to contacts, hit the menue button, and go to filters (play around with that because i cant remember off the top of my head how to change it or what to change it to. 2nd how many messages do you have on youre device? if you store a lot of texts, and mms on youre device then youre device could start deleting contacts. 3rd how many pics/ring tones do you have down loaded? if you have them saved to youre devic memory instead of an external memory card (micro sd) then youre device could start deleting contacts.4th have you ever synced youre device with blackberry desk top manager? if you have not, then i would recomend doing that, if you have not down loaded it you can find that at this link :http://na.blackberry.com/eng/services/de…
(blackberry.com,software.desktop software for pcs)
chose down load now, v.4.7 with media manager (the best version so far) foolow the steps for syncing, and creating a back up file.
if you do sync to youre computer, who do you have set to win on a conflict? you can check that by going to sync>configuration>syncronize>sync settngs> in the desk top manager. if all of that is set as it should be...... do you have the most up to date software on your phone? you can check that by going to options and about on youre bb device.