Dollar General complaint: Given false information and no help rectifying situation

On Friday January 13, I had visited the Flat Rock Dollar General Location on Gibraltar Rd, I was buying party supplies for my gender reveal party the next day. One of the main items I needed was a helium tank to be able to fill up my balloons, I looked and there was only one tank left on top stock halfway down the aisle and the box was severely damaged. I was questioning on buying the product scared that it was returned because of its condition. I took it with me to the register to speak with the employees about it, the employee reassured me that it was fine, and box was just damaged from the truck and if it didn’t work i could bring it back with my receipt. I decided to trust employee’s judgement and bought the product. At the party the following day I opened helium tank to find it was empty and would not work, almost ruining my party I had to rush and go spend another 40 dollars on another tank. Sunday, the 15th I returned to the dollar general to get my money back for broken helium tank as I was promised by employee who was there, and he said the general manager would help me at the register and he left for the day. When talking with the manger she was rude and unhelpful, and refused to show me any kind of understanding for my inconvenience. Now I am out 30 dollars and stuck with a broken empty helium tank and will never return or give my business to Dollar General again.