If you are familiar with deleting applications or wiping the BB then to answer your question, Sprint is correct. You will need to download Blackberry Desk Top manager to reload from a wiped BB. Apparently the text or messages application is possibly corrupted. Sometimes updating a blackberry will not completely clean the corrupted application or parts of the core OS. You can also use one of two free programs to assist. Blackberry Swiss Army Knife or JL_cdr. JL information is available on this forum by doing a search. Although your issue may appear to be only a text issue, I have included a link to RIM's info on duplicate messages. Text is a form of email messages and some may help with your understanding of the issue.
KB13528-Duplicate email messages are received on the BlackBerry smartphone