E-mail Transition Failure

Since my e-mail has transitioned to Yahoo, I am losing e-mails.  E-mails that I have been getting forever are no longer getting delivered, or very sporadic.  See below for examples of e-mail concerns.

1. E-mails from Amazon when placing orders; sometimes they get to me, but most of the time not being delivered
2. E-mails from Generac when the generator operates; same as above for Amazon
3. E-mails from friends; one friend sent me an e-mail 5 times before it was ever delivered

I try to call Yahoo and all I get is a recording saying there is an extremely long wait an to try calling at a different time.  It does let you hang on, but I final gave up after 2 hours.  This is totally ridiculous.