I had W-2 from 2019 but my old employer won't allow me to get it

You will need to contact your employer in order to get your W-2.  

 If you still don’t get your W-2, contact the IRS and tell them your employer didn't send it. You may call the The IRS toll free number is 800-829-1040. 

The IRS will send your employer a letter requesting that they furnish you a corrected Form W-2 within ten days. The letter advises your employer of their responsibilities to provide a correct Form W-2 and of the penalties for failure to do so.

The IRS will send you a letter with instructions and Form 4852  Substitute for Form W-2, Wage and Tax Statement, or Form 1099-R, Distributions from Pensions, Annuities, Retirement or Profit-Sharing Plans, IRAs, Insurance Contracts, etc. You can use the Form 4852 in the event that your employer does not provide you with Form W-2 in time to file your tax return. 

If you’ve attempted to obtain your W-2 and are unsuccessful, you can file using a substitute Form W-2, Form 4852.

Talk to Your Employer

there is no requirement for an employer to furnish you with a second copy of the W-2.  you are talking W-2 and not 1099?  I ask because you are using  self-employed version 

this leaves you with several options

go to IRS website, register,  and  then get a transcript for 2019. it should have your W-2 info, but not the state info

go to the social security adm and request a COPY. THERE'S AFEE AND IT CAN ONLY BE DONE BY MAILING IN A REQUEST

https://faq.ssa.gov/en-us/Topic/article/KA-02501