[header] How to deactivate onstar [title] Contact onstar. [step] If you want to cancel your onstar service immediately, you will need to contact the company and speak with an adviser. [substeps] The simplest way to speak with an adviser is to press the blue button on the onstar system installed in your vehicle. 
Alternatively, you can contact onstar by phone by calling : 1-888-4-onstar (1-888-466-7827). After contacting onstar, the adviser you speak with should be able to guide you through the process of canceling your service.