Airtel Prepaid — activation

i recently shifted from my postpaid no. ( since last 5 year ) to prepaid lifetime . but after few day - it is now showing sim card authintication failed so. i had taken duplicate sim also -- gaain message is same - but when i contact call centre - no . is active -- moving from dealer to offices airtel ... please do require action no.- is [protected] alternate no. is [protected]