I never changed anything on my taxes, been at my job for 2 years 6 months and they recently removed my federal income tax. And I’m just finding out. What do I do?

I never changed anything on my taxes and looking back they changed my deductible to 30,000 yet I have Zero children and I personally never made any changes and they don’t have any physical paperwork stating I needed a change. The person who worked Payroll/HR quit last year and now I owe 2.9k