USB problem

i bought a usb which is working properly for the last 2 mnths.. but now there are some problem which it have during saving data..the prob is that when i save the data there will be no error bt when i open the usb on the other computer there is no data.and the size os 0kb in used and 0kb in free.. i also format this soo many times but the problem didnt solved.. and the 2nd prob is that i lost the invoice soo it means i cant claim its warranty soo what i should doo???

Many Of the uSb's I myself witnesses being currupted , peaple usually claim it to warranty but u dont have invoice . Did u scan it for viruses ? Check your PC for viruses , U format the uSB then again virus enters into USb cause ur PC contain viruses , try AVAST antivirus to remove it..