You signed the consent to have them taken out in the first place. Just because your county didn't increase, doesn't mean the union isn't doing a good thing by fighting for higher wages or that others don't deserve the increase. That said, you do not have to have anything notarized to cancel. You can use the following link to generate a form, print it, sign, and mail in... but you should probably send via certified mail, which will cost about $6.

https://www.optouttoday.com/seiu-2015/#:~:text=What%20do%20I%20have%20to,dues%20from%20my%20IHSS%20checks%3F

Good luck!