Family Dollar complaint: Short me on cash

So me an my boyfriend went into the family Dollar in Milton fl next to Milton high school. An we got TWO THINGS sour stittles for 2.50 an ibuprofen for $1 total was $3.68.. I gave the lady $20.68. me and my boyfriend were in a rush cuz I had to drop him off at work it was 2:41 pm when we checked out . Well we went to Dollar general because family Dollar didn’t have what I needed when I was checking out at Dollar general I realized that I’m missing my change from my 20 not thinking that the cashier didn’t even give me my change back! So I looked at my receipt she cashed it out at $3.68 I went back there and I told the cashier I said hey I was in here like 10 minutes ago just realizing that I didn’t get my change from my 20 she wanted to argue with me saying that I gave her the exact change and that it turned around to be oh I gave you your change back and I said no you didn’t you put in the register 3.68 it says that on my receipt! As she rudely told me that I needed to move with her hand so she can ring up the two people that was behind me before she can take care of my issue she was running her mouth saying that she didn’t owe me no money to the customer she was ringing up! So she finally comes over counts down her two and realize oh she was over on her register so I told her well I gave you $20.68 and the total was $3.68 you owe me $17 she only gave me $16 back and wanted to raise her voice to me saying that she can’t give me the extra dollar because her till is saying that she is $16 over all this BS so I just looked at her and said I understand it’s a dollar but this is not my money and it’s hard times right now she was very unprofessional and I hope she is not a manager because there are other ways for her to resolve that problem because I’m a store manager at Dollar general I know how things work I don’t know her name because she didn’t even have a name tag on I just know what time it was I was in there and what day it was and there was only two people working. I WILL NEVER EVER GO BACK INTO THAT STORE AGAIN THERE HAS BEEN MANY COMPLAINTS ABOUT THAT STORE AND HOW THOSE CASHIERS ARE!