National Highways Authority Of India [NHAI] — Charged toll fee when there was sufficient balance on fastag

Today I went to vellore CMC hospital from Chennai, when crossing the chennasamudharam toll plaza in the morning my fast tag was working fine and had a balance of Rs.500. When returning back to Chennai, toll booth workers said I dint have sufficient balance on my fasttag so have to pay for crossing the toll. Now after crossing the toll in fasttag also my money got deducted as well as I paid Rs.50 for crossing the toll. Pls guide me in resolving the issue.