bog box irritation

So today I was out doing some shopping, I needed a few items for the house, and while I was out I decided to pick up my new digital converter box to convert a digital signal for use on an analog tv. Our wonderful government recently started handing out $40 gift cards to people that request them to help offset the purchase price of the converter. (If you want more info on this check out the link above.) So I was pretty excited that my gift cards arrived and now I will be able to pick up a few more stations since I don't have cable. Unfortunately there aren't many stores that carry the converters but wal-mart and meijer both were listed as stores participating in the rebate program and both are near-by so I checked wal-mart first. Three months ago I said I was never going back to the wal-mart on colerain ave, the store is always a mess, there are hundreds of shopping carts in the parking lot and they never have enough staff to run the registers or do other things, but today I figured I'd go back and give 'em one more shot. Well it was exactly as described above, it was saturday and only 4 or 5 checkout lanes were open, the lines were huge and they weren't moving so I turned around and left. I went to my trusty target store which has never let me down and they had all that I needed except for the converter which I knew they didn't carry. After that I decided to head on over to the Meijer store on Colerain which also three months ago decided I was never going back because they did not have what I needed. This only applies to Meijer on Colerain the others in the area have been fine. So I went expecting little, but figured it was worth the try. I found the converter box, made sure it was one that qualified for the discount and headed to check-out, however at the register the manager proceeded to tell me that they did not accept the gift cards from the government and that I should go to wal-mart. Two things about this really ticked me off, first the manager didn't care that I traveled specifically to his store at the recommendation of the government to buy a product with government money!( its surprising because I'm sure there's a big profit on the item because the government always over pays!) and second he told me to go to wal-mart!! What kind of manager tells you to go to the competition for something he has in his store? That was a first for me, I proceeded to tell him wal-mart was not getting my business and at this point neither was Meijer! I again left all my products and the register and went home in a grumpy mood without my converter.
So my question is when is it appropriate to write a letter complaining about bad service? I think I'm going to write to both wal-mart and meijer and I'm going to see who responds faster. I'm not looking for a free handout and I'm going to let them know that I'm simply looking for a retailer to care about their customer!
On another note, is this really a big deal? should I care about what a store has or doesn't have or should I simply blow it off and go elsewhere? am I just wasting my time getting irritated at a giant corporation? I feel like lately I've been a grump inside, I'm not sure that anyone else has noticed it, at least no one has mentioned anything to me, but things like this make me feel like I'm going to turn into a grumpy old man someday and thats not at all where I want to be. So for now I'll write my letter for the fun of it, and I'll do my best to not turn into a grouch! and I'll definitely boycott colerain wal-mart and Meijer until the next time its 3 am and I need something!