National Highways Authority Of India [NHAI] — excess amount debited

I was travelling through dankuni toll plaza on 2nd mar 2019, rs80 was debited from my fastag account. While returning again rs80 was debited whereas it should have debited rs 40 as return journey as cost is rs120.
Fastag id:34161fa[protected]
Vechile no: wb24an8032. If this is the service then why govt is encouraging to use fastag. When we return within 24hours then (Total of return journey)- (Amount debited) has to be debited but in my case once again amount for single journey has been debited from my account.