Employer sent me a 1099-NEC for my last paycheck when it should have been included on my W-2 income (and I’ve already filed my taxes, because w-2 was all I needed)

I received a 1099-NEC today. However, the income reported on the 1099 is incorrect. It should have been reported with the rest of my income on my W-2. I have been unable to make contact with this employer for the past several months (regarding other problems such as unpaid wages) so I am assuming, I will not receive a response or be able to get this fixed. 

I’m nervous now that this will cause issues and also cause my refund to be held up. Do you think this will happen? What do you advise me to do? The 1099-NEC was only for $800 some odd dollars (which was actually the amount of my last paycheck from this company, but I was still technically employed during the dates I was being paid for, is this legal for them to file this as contract work, when I had signed a job salary offer that clearly states I was a W-2 employee?)