Q: How to prove prior work experience if it is not provided by prev emplo

Hi Sir/Mam, My current employer wants to file GC for me, but he said I need to prove that I have at least 1 year of prior experience through formal experience letter, as USCIS no more accepts the secondary evidences like, paystubs, offer letter, notarized affidavits from previous colleagues, etc . Unfortunately, my previous employer is not willing to provide me any experience letter whatsoever, he is not even replying to my emails. Can you please tell what is the situation actually and if it is true what my employer is saying? How can I still prove that I do have more than 3 years of relevant previous experience? Thanks with regards.

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