Quarter full product

I purchased minoxidil, the item felt lighter than usual and when I went to use the product I noticed that the bottle was very light, when I opened the bottle it was quarter full. It's really frustrating since it's such a busy period and you have to stand in such long lines to receive bad service then realise your product is probably a used item. And being served by the manager who needed to create another profile as she couldn't search correctly is another frustrating part, being a manager you'd know your products how can you not realise you're giving someone not a full item. Absolutely frustrating!!!