Using any coupons requires thought, even with your infant. 1) Group items, with the coupon visible, at the end of your order. That way your undivided attention is on the register.
2)Stay calm, keep your receipt and then, when time allows, review, photocopy and voice your concerns to the manager.
3) Be nice and refrain from using extreme accusations. This trivializes your legitimate issues.
4) I am under time constraints and being next in line, ready for business (coupons at hand, payment set to go)I don't appreciate your lack of planning.Saying that, all the best.