There's very little that you can do on your own. The phone most likely needs to be reprogrammed - i would take it to a Sprint corporate store that is a service and repair center
other expert is backing this answer
I have been with a major cell phone provider for over 3 years working directly with customers in both technical support as well as billing. I handle all types of phones from basic phones to smart phones such as the Iphone's and Android's. I work in the call center so my average day is spent talking to and handling customers issues.
I have also worked for a major bank in both the retail (checking savings) and investment side for 6 years before switching to a major cell phone provider during a merger in which my tenure was not senior enough to keep my job.
I enjoy researching and helping customers and I enjoy finding solutions through all avenues available to us.
Does it happen to you constantly in the same area? Or is it more of the same people keep sending you mult. the same text over and over? If it is more of you getting the same message over and over while you are in the same coverage area it could be you leaving and re-entering the network again and again. I've seen this problem happen it areas with poor network and where people use airaves. The same could be true for the person sending the message. If they are in bad network when they send it, it tries to resend over and over. Your phone may be perfectly fine and it could just be a issue with the network. I would first try what the other 2 suggested, try a battery pull, then try reprogramming your phone. If that doesn't work bring it to a repair center to they can run some tests on your device. If they come to the conclusion that your phone isn't having any issues, its a network issue. To get a network issue fixed, you have to address it with customer service so they can make a ticket and have a tech fix the tower.
I have worked for Sprint for more then 7 years. I have held a number of positions that make me the best possible choice for fix or address some of the potential issue you may have. I have knowledge of what causes many of the error customer encounter.
You can log into your Sprint account and block the number that the message is coming from. If it is come from someone you want to receive text messages from call 8882114722 and tell them you are receiving duplicate text messages.