Misleading signage

While in woolworths 2 days ago, there is a sign up on shelf advertising Lays crisps for R8.50. When they ring up at the till, they charge R14.99. I only see this after I have paid and take it up with manager. She says the ones I took are not on special only the 125g packets. Mine are 110g. So I ask her to exchange them for the correct ones, but she tells me they are out of stock. WHY on earth do they put up a sign at the incorrect item, advertising something that is out of stock??? So again in woolworths today, a sign up on the shelf at the button mushrooms that says buy 2 save R10. They are marked 20.99 per packet. When I get home I check the slip only to see that the discount was not app****. I called and spoke to the manager of the foodhall, Tsesha, who advises that all the other mushrooms except the one's I took are on special. When I asked why the signage is up on the shelf where these were, she tells me she doesn't know and I must bring them back for a refund. As I don't just live around the corner, it will cost more than the R10 to return the mushrooms and have nothing to show for it!!! Whatever happened to the policy of what you see is what you pay??