Prices on the shop move with promotions and bundles, and it is genuinely irritating to see the thing you just bought get cheaper.
If the price of something you ordered dropped shortly after you bought it, message us here with your order number and what you saw, and a colleague will get back to you on this.
A related point that is settled policy:
Discount codes cannot be applied to an order after it is placed — see I forgot to add a discount code. Message us here with your order number and the code, and a colleague will get back to you. The welcome code does not apply to sale items or bundles.