You can text 9999 and use the code for allowing short codes (essentially removing the block). The list of options available when texting 9999 is located at this link http://support.sprint.com/support/article/Block_or_allow_text_messages_from_your_phone/case-cx832318-20091103-160141. Let me know if you need further help as I have some tools on my end that I can use.
Help prevent distracted driving. Get Sprint Drive First FREE at the Google Play Store.