very sad and unhappy

our company pays this book shop , a certain fee for us to purchase books. in July I bought few items with that money and the lady at the store made a credit purchase for me that I didn't not ask for. and i'm now owing the store the same amount that I thought was left kn my busary. prior to the purchase I aksed how much do I have availbel to buy with she said its R3500 so I assumed that money was taken from that R3500 that I had available. I bought without knowing I was buying in credit their debtors department phoned me and asked me to pay back the money and I was like " which money because bursary payed form me.im very unhappy and i'm not going to pay it the one responsible for this must pay it otherwise I will take this further. please investigate because if this continue happening a lot of people will suffer. this happened in Durban bramfisher branch