Wrong Decoder

bought a decoder with game with free installation on Saturday morning , the staff tells me it will be installed around one o'clock and ill have to be home. installers get to my house on Monday evening to find i was given the wrong decoder and there was suppose to be a voucher inside, when i get to the store the employee apologizes cause he still remembers me and says the manager will assist. when they call Gram (manager ) he tells the employee over the phone he cant do anything because i lost my slip. i asked to speak to him then i was told he was busy with promotions. i decide to leave the decoder there, they can keep it because i have no slip, they should resell it for all i care. why would i go through all this trouble to lie about free installation? i was told it was my fault for loosing the slip and i left the decoder there because even Grams staff felt like it was unfair. As a manager at lease pretend as if you care or there another option and not tell the customer its their fault when the security also was suppose to check if the bar-code from the slip matches the one on the box!