I received a letter from the irs asking me for a copy of what I worked for 2019 . I don't have proof of working for that year because I didn't file . I made less than 500

Your post is very confusing ... you mention 2019 and then say you put the 2020 income on a 2021 return which is not allowed.   So what exactly is the IRS letter asking for you to provide and for which tax year ? 

So your saying I couldn't file my 2020 1099-G with my 1099-G for 2021

Each tax year has to be filed separately ... 2020 income  only goes on a 2020 return and  2021 income goes on a 2021 return  ... they cannot be added together on one return.  If that is what you did you have the IRS confused.  Send them the info they are looking for with a note explaining your error.  

very confusing.  you may have 2 issues. one is putting the 2020-1099 on your 2021 return and the other is that the IRS wants you to verify your identity.  the request for 2019 info may be part of the verification process.  if the IRS wants identity verification and you're due a refund for 2021, you won't get it until you comply and furnish the info requested.

Did you have any income of any type in 2019?  If not, were you a dependent?