Family Dollar

I purchased a heater a few days ago. All of them were opened so i thought nothing of it. I go to return it today and they tell me i can't return it because its opened. Well i want my money back. It was already opened. I showed the lady in the store that all of them were opened. All of them. Just like they were when i purchased it. I did not use it. So you have a policy that it can't be returned of opened but you're selling it opened ? This is not ok an i feel scammed. I'm very upset. This should be illegal. How is this possible. The box was opened when i purchased it. There were 3 in stockwhen i returned it. Which was also opened as i said. Then, the employee ripped the box up badly taking it out and putting it back in. Now i have a brand new unused heater with a ripped up box. I'm dissatisfied highly. Dollar General employees have never made me feel this way