How will I know if my employer already filed me an immigrant visa?

I'm a nurse with all the needed requirements (except visa) to work in the United States. I recently got my NY license. I have 2 agencies. I am in doubt of the 1st agency because they told me couple of months ago that they already filed me in US embassy, but I still haven't got any proof (notice of receipt). I followed up my request couple of times, but they always fail to give me a copy of the certain document. My 2nd agency already interviewed me and said that they will be processing my immigrant visa, but i'm quite puzzeled about it.. I don't know if it will cause conflict. So i like to know if there is an available option to check my status (if there is) in US embassy. Thanks for your reply!

Anyone who has filed paperwork for you should give you copies of the documents showing the receipt number. It sounds like you're applying with overseas agencies. If that's the case, I would contact the embassy and ask if anything has been filed on your behalf.

Multiple filings do not necessarily conflict. You can file multiple applications and see which one goes through first. Having an application for a visa approved does not guarantee that you will get the visa, so having multiple applications approved isn't a problem. In the end, you'll only get one visa, so you may have to choose. The only problem might be if you are filing for mutually exclusive visas (e.g., one immigrant and one non-immigrant).

Wouldn't you have had to sign something for them to file?

You can track petitions at uscis.gov generally, but you need some information. If I were you I would contact uscis.gov. There are a lot of scams out there.