Group discount services - typical communication problems

Samples for the sake of his wife bought several discount coupons in the Ukrainian "Pouupone". Logically, money was paid for a certain service - a discount on certain goods at a certain time.

Today, there was a desire to use one and order sushi from Sushihoum. And here he faced a phenomenal statement, the possibility of which had already been weaned:
- the terms of the action have changed, because the discount now applies to a much more limited set of products.

Those. you buy a discount on the goods you are interested in, and you hop: "but we changed our mind and now the discount on these goods does not apply."

“Sushihoum” nods at “Poupon”, which was supposed to inform me about changing the conditions of the action, although the question itself: the one-sided reduction of the service, for which it has already been paid, gives a frank cheat.
')
With this approach, sales services for group discounts will develop long and painfully for us ...

UPD: As in many similar situations - the problem was in insufficient communications. Bucket actually notified the supplier by email. But only. Given that the service of mail by mail is a stream of announcements of new discounts, this letter did not attract attention even once. Find on the site the same phone support was unreal.

What can and should be done to prevent such misunderstandings from causing conflicts?
At a minimum - bring the phone around the clock support home.
And in the customer's box, either make changes to the discount coupons already purchased, or add a new coupon with a new address of use.

Moral for everyone: Do not expect that all customers read all mail.