Computer World against buyers 2

Hello, hello. I'm sorry to speak to you, but ...

Two weeks ago I published the post "Hewlett Packard and Computer World against Buyers . " In a nutshell: my friend went to the store (unfortunately, it was “Computer World”) for a cartridge to her photo printer. The saleswoman gave her a cartridge, making sure that he was 100% suitable for her printer. However, the cartridge did not fit.
Here I connected. In order to help a friend, an in-person meeting was held with the store manager and with the saleswoman, who for some reason suddenly began to blatantly lie, claiming that "she did not say that." After half an hour of unsuccessful butting, a statement was written addressed to the store manager. Yesterday the answer came, as it is not difficult to guess, negative.
Honestly, when I wrote at the end of the last post “I would hope for the decency of the store manager,” and I read it myself, I smiled involuntarily. Well, really, what decency can a director of a store like “Computer World” have?

In general, I believe that this is disgusting - to deceive customers. And I consider it a shame that the director did not bother to sign our statement for two weeks. It may seem that 807 rubles is not so much money, but my friend is a student, and for her this amount is not small (she bought a cartridge with a scholarship). Personally, I have already decided for myself that in case of a negative outcome of the case, I will give her the money. I do not mind, but she will be pleased. However, I would like to bring the matter to the end, and to do everything in my power that justice would triumph.
I asked for a personal meeting with the store director, but they refused me. What else can be done, where to turn? I ask for help of the community. I wish that this case would not go unpunished.
Thank.