Yeah... you really need to send them more than just one or two. I'm sure they get a lot of emails and it would be easy to accidently overlook one or two sometimes.
I know it happens to me sometimes... and I accidently overlook or misplace an email from time to time.
Also, what kind of questions did you ask in your email? If they get the same questions day in and day out in emails, they may not respond to all of them... as it would be redundant.
Give it another try or two and see if you get a response. Also, you may want to try giving them a call as well and see if you can get through to someone.
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