Self Employed and references for USPS

I rarely post in this reddit thread but I am curious on how to get References when you had been Self Employed for a couple of years.

I was contracted for three -four years but my last employer never inform me their most recent phone(there phone number often changes and was known to have a high turnover rate. So how do I use them as my reference when the last reference is almost ten years oldmpany or had left the company a while back