A O Miller Exxon

I recently filled up at the Exxon Station in Katy, Texas. (DLR # [redacted])The posted price on the sign and at the pump for regular gas wa $3.19. After completing the fill, I noticed on the receipt that I had been charged $3.39. The attendant informed me that the posted price was for cash only, yet there were no signs or notices indicating that I would be charged more for using a credit card. The station next door posted $3.15 for cash and $3.19 for credit. I feel that this is a deceptive practice and a considerable overcharge. This resulted in an overcharge of $4.32.