Sbi Fastag — Suspicious debit of Rs 240 today as debit adjustment in addition to payment of all charges

I have been travelling from chennai to Thanjavur and paid all the five toll charges. In the end, I was left with Rs-23.49. Immediatly I recharged with Rs 1000 and the negative balance has been debited and left with Rs. 976.51. Now after a week, there is a debit of Rs. 240 in my fastag account in the name of debit adjustment. I just wanted to raise this issue with relevant authorities what is meant by debit adjustment when I paid for all the toll charges. Im ready to share the proofs with the concerned authorities.