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Go to System Preferences / Network make sure Ask to Join new networks is checked then click on Advanced and remove any networks from the list you do not want to use any more. When you are back online I can check your system by remote if you wish and I have other things you should do too. Let me know
You can also remove any entries for old wifi networks from Keychain. You can do the below:
Search for the older Wifi names
Right click and delete the entries
Hope it helps.