Airtel Fastag — Fastag blacklisted

My Airtel Fastag account is blacklisted at NPCI by airtel bank in spite of having sufficient balance. I wrote to wecare customer care and made 30+ calls to Airtel customer service. Every executive said to me, you problem will be resolve in next 48hr. After 1 month, my fastag still blacklisted. Airtel does know how to resolve this issue.