How to clean my sterling silver necklace?

I have a sterling silver name necklace and it's about 5 or 6 years old that I can't seem to get it shiny again. I have tried the cleaner you buy at Walmart, baking soda, toothpaste, and even asked the Kay jewelers people about it but it still has this brassy dull tint look to it. I asked the Kay jewelers people if there was a way to redip it in silver or maybe rodium plate it but the guy said it wouldn't work (but he didn't really seem to know anything in my opinion) but anyways I'm going to get a second opinion. Does anyone know what I can do? Is it even possible to rodium plate or redip a silver necklace? I really love this necklace and do not want to give it up but it's just so dull looking. Help?
Thanks : )

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