your friend may be pranking you lol xD check if someones been fooling with adjustment button. the polaris spot meter i use has it under the battery cover. yours might be in the same spot.
if that doesnt work, try the shake test, and see if you hear anything loose rattling around, maybe a little piece of plastic floating around inside sphere and messing with readings?
if its really bonked out, it might be cheaper to buy a used meter than trying to send it for repairs.