Did you pay cash for that phone? That's the only reason I can think of why they would tell you 4-6 weeks, if the store doesn't have enough cash on hand, they can only mail a check.
I'm sorry your phone got damaged, unfortunately protective covers manufacturers don't state or imply any sort of guarantee that their products will protect 100% of the time.
I recommend contacting a local independent repair shop to get it fixed.
Dmitriy