Go into the Bing Maps portal and check your usage reports. Free accounts have a limit of 125,000 billable transactions a year for free. You can find documentation on how to view your usage reports here: https://learn.microsoft.com/en-us/bingmaps/getting-started/bing-maps-dev-center-help/understanding-bing-maps-transactions#viewing-usage-reports
You can try and create a new key, but it's likely that your account is blocked if it has gone over the free limits.