I recently bought some nappy bin cartridges from Amazon. They are marketed as a pack of 6. The pack of 3 is on sale for £9.99 (normal price £13.99). A single cartridge is £3.37 (normal price £5.49). Pack of 6 £19.99 (normally £21.99).
So normally they are the cheaper option but on sale they cost the same per unit as the 3 pack.
However the box has now arrived and splashed right across it is a red manufacturers label which says '4 + 2 free'.
So basically Amazon have charged me the unit price for the 2 free ones by selling the box as a pack of 6. Are they allowed to do this? I don't know if it makes any difference that I am not in the UK, although I buy from Amazon UK. If not, what should I do about it?