Email or Certified Letter or Both?

Thank you very much for the advice on this forum. I am currently about to take the first step in stopping the pdl from hitting my account.

I know I need to coordinate closing the account and sending letters to the companies. OhioGal mentions just emailing them. Is it best to send both an email and certified letter or is the certified letter a complete waste of time?

What are people's experiences recovering overpaid loans with just emails? How many follow up calls/emails do people who actually recover overpaid loans require?

I just want to confirm all these are illegal in California:

American Web Loans
Ideal Gelt
Cornerstone Financial
Cash Yes
VIP Cash
Plain Green Loans
Vista B
Mobiloan
Mesa Financial

Thank you so much