JM3030 said "You can by pass the store manager and get a hold of head office. Thats probably your best bet, if you haven't tried that already.
Was it a curb side pick up? If so, it was picked up (not just ordered) while the sale was still on? "
Is is probably your best bet.
Also, I've had issues in the past of a particular store not honouring sale prices on their curbside service, even though I ordered and picked up in the same sale period. It wasn't enough money to make a stink about it (and it was an item I needed anyway), but I watch it more closely now.