What is the Islamic legal ruling concerning the loss of an item purchased from a store, and is it permissible according to Sharia to take a replacement item without sufficient evidence?

The burden of proof falls on the claimant when the defendant denies the claim. Since the employees believed you, there is no blame upon you. We advise you to seek refuge with Allah from Satan and to turn away from whisperings (waswās). Also, frequently recite the Quran and observe the morning and evening remembrances (adhkār), for whisperings are from Satan, and there is no way to overcome them except by seeking refuge in Allah.