Widgets will not delete

Hello everybody, I have a big problem well 2 problems really! 1st one is my widgets i deleted will not disappear from my footer, i tried to add blank text as many have said to do so on here but it did not work, but those widgets only show on certain pages not all
website is

https://www.georgechomakov.com

i want to get rid of the subscription widget and the picture on the bottom of some of the pages please help if you can…

also i want to be able to have a thumbnail where ever I post my website, how can I get one so when i post it , a thumbnail shows up?

thank you for your time