Clinton Chevron

I purchased gas on 12/01/around 7:or 8:a.mand I tried to pay at the pumpI received the message to see cashierI took my card in the store and the cashier who was a foreign male asked me how much did I need and I told him He stated that if it didn't take the whole amount it would go back on my cardThe amount that my card was charged was Then they took an addition after that transactionI contacted the store as well as my bankWhen spoke with the manager as he stated he was, he told me it was nothing he could do about refunding me my I feel they are talking additional small funds from customers accountsI would like my money back as well as the store to be investigated Someone please help in this matter