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If you recently applied for an account at a CU or bank, and there was negative information in your chexsystem file that prevented you from opening an account, they would have to legally provide you an "adverse action" form stating that was the reason. You can then ask for their findings.
Chexsystems only mails you results of your request, and is a legitimate site.
Is this where you went to get it?
https://www.consumerdebit.com/consumerinfo/us/en/index.htm