Creditor comfirmation sign by wrong person due to mistake

AO demand creditor confirmation during scrutny . my books show one party santoshi traders prop kuwar sing amount of rs 2 crore. i prepair cinfirmation and mention pan number correct of kuwar singh for example ABDFS4590J . office boy due to mistake sign the comfirmation from another party krishna traders whose pro
p was narender kumar and same is submit to AO. during tha hearing ao find that fifth letter of pan number i.e. (S) does not match with the sign of narendra kumar. and AO make addition . kindly tell me any case laws on about this matter