First off, I would take the LG phone back to the store and speak to a manager. If a sales rep told you it might be that your older phone doesn't work he/she is clearly just trying to sell you a new phone. The S3 is in the Fitbit list of supported devices and Best Buy should know that. In addition, they should also know that Windows 10 is supported so should not have simply surmised that you needed a new phone.
As to your problem, it is also possible the 2nd tracker was also defective......... but not very likely. It sounds like you have done everything that you should be doing, but clearly you have not. Without actually sitting with you and watching I can't really say what you are doing wrong. I would suggest you call support and get someone to walk you through it instead of relying on chat.
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