Termination blues

Hi.

I received a termination letter from my past company. The reason was, I sent my resignation letter from home and responded only when they reached out.

I know I am at fault. Should have sent resignation from office itself. But their punishment seems very harsh. I didn't get a chance to explain myself.

Wherever I am applying for jobs, getting turned down as I do not have experience letter and relieving letter. Having a termination letter seems to be equal to having a criminal record.

I tried requesting my ex company, but seems they have forgotten my existence, and talked in a rude manner.

Day by day I am losing confidence. Trying my hand at freelancing also, but it would be like starting from zero.

How can I repair my situation. Advice pls.

PS: Humble request to all, no trolling please. Already I am down, don't want to get out.