Macshop extension virus

Help! I got infested by an ad company who installed ads in my mac safari without my consent after installing a program called Weather Live which I bought on the app store and I tried to uninstall the Macshop ads after a suggestion to go to safari extensions and just remove it. many people claim that this worked but apparenty did not work on mine as the macshop extension is not listed in the extension lists also I'm baffled why Weather Live still re-installs even though I deleted in the AppCleaner.. Im at wits end to solving how to remove these parasites out of my mac 😠

many thanks,

Tim