Is it legal to withhold final paycheck/vacation pay to repay relocation fees in NC?

Hi there.

My former company payed for my relocation from Michigan to North Carolina back in April of 2015 with a 2 year commitment. They terminated my employment on July 21st of 2016. Now they are withholding my final check "in order to begin repayment" of those fees. Leading up to my dismissal (I had a feeling it was coming) I started asking for all the documentation that they had when I signed with them. I spoke with several departments (HR, Talent Recruitment, etc) and they were not able to produce the letter where I agreed to pay anything.

So I have several questions...

1. Do they have the right to withhold that final check?
2. If they were not able to produce the documentation when I asked for it while I was still employed, are they still able to collect these fees?

In addition to all this I'm in the middle of a bankruptcy would I be able to add this type of debt that?

Thank you for your time,

Tom