SADV took money from my account even though I had payed with cash at the bank

I really like the way it's fast with the internet access and stuff but during the first month of using the WiFi I payed the exact amount at the bank and everything was fine but now this is my second month using it and I payed recently and I thought everything was oky but when I checked my money balance in my account I noticed that they took more money even though I had payed at the bank with cash so now what I'm trying to understand is that why did they take more money if I had payed them already with the money transfer at the bank