Spilled Paint

I went and purchased paint at Jack's Paint on 17 January 2015 at woodmead, I bought 2x 20l one was sealed the other I wanted a different color and they mixed it up for me. On my way home I started smelling paint but didn't think much of it. Upon my arrival at home the mixed paint had fell and spilled in my car boot. I called them and was told it's impossible that the paint would spill as they properly close their containers, but I told them it did, how come the other one didn't fall and spill? Since it was Saturday and the store was about to close I was told I can come back on Monday. Upon talking to the owner on Monday he told me since he's part of the franchise he'd call me the next day and told me once the seal is broken when they mixed the paint container won't go back to normal and could possibly open though it's rare. I'm of the opinion it wasn't closed properly as they claim. But since the 18th of January I've been following up they taking me from pillar to post. I tried cleaning my car but it's messed up and he had the audacity to question why I couldn't get it cleaned. These people are ***** and don't want to take any responsibility. Totally gutted!!!!!