What do you mean, "When I add a company and change the company name". When creating a new company in the UI, HubSpot should prompt you if there is a match. If you click "No create a new one" you are telling it to create a new company, not update the old one. If you click on the company record and change the name, it shouldn't be creating a new record, just updating the existing one.
When adding contacts, if you have the setting on to create and associate companies with contacts, HubSpot will create a company anytime a contact is added and their email doens't match an existing company domain. If you have contacts that have a slightly different email domain than the company record, you can add additioanl domains to the company so it will match on multiple email domains.
What do you mean, "When I add a company and change the company name". When creating a new company in the UI, HubSpot should prompt you if there is a match. If you click "No create a new one" you are telling it to create a new company, not update the old one. If you click on the company record and change the name, it shouldn't be creating a new record, just updating the existing one.
When adding contacts, if you have the setting on to create and associate companies with contacts, HubSpot will create a company anytime a contact is added and their email doens't match an existing company domain. If you have contacts that have a slightly different email domain than the company record, you can add additioanl domains to the company so it will match on multiple email domains.