Let's get to the first question: "How long will I be banned from entering US?" - I assume you entered the US as a F1 holder with an I-94 that states "D/S", meaning Duration of Status. The moment you violated your F1 status by dropping out of school, you went Out of Status. A F1 holder does not accrue unlawful presence that triggers the 3 year or 10 year bar from entering the US until an Immigration Judge (IJ) or a USCIS officer makes a determination that the F1 student is Out of Status.
The F1 holder starts accruing unlawful presence from the date that determination is made not from the actual date he/she went out of status. If the F1 holder continues to reside in US for over 6 months from the date of the determination, then he/she will be barred from entering the US for 3 years after departure, and 10 years if he accrues over 1 year of unlawful presence. Also, note that a waiver may be available for a 3 or 10 year bar depending on certain factors.
I will suggest you look into the Deportation Order mentioned by your friend, based on the fact of this case, I'm confused as to why you should have one without a criminal record. Naturally, DHS don't go after illegal aliens unless they are high priority to them, (for instance, people with criminal record). Ask a relative or friend in the US to check if you actually have a Deportation Order. If you do, you will need the assistance of an Attorney to see if a Waiver may be available to you in order to re-enter the US.
I doubt you are inadmissible but the visa will probably denied to you in discretionary grounds.
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It is unclear whether you were subject to removal proceedings. When you moved, you probably did not update USCIS which means any notice was lujelt sent to your old address. If you were ordered deported, you are subject to a ten year ban. You would need to seek a waiver. You should resolve the way issues with the credit cards.
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Obtain your federal records to determine whether you were deported. If you have an A#, information might be available sooner, by phone. If you were removed, you face a 10-year ban and would need a waiver to reenter sooner.
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