Sometimes occur that a specific SSRS subcription is in pending or blocked or using too time to create report. if you want to force the stop of subcrption you can do it using this two string of code directly on sql database of report server:
truncate table [ReportServer].[dbo].[ActiveSubscriptions]
truncate table [ReportServer].[dbo].[Notifications]
Done that your Subscription is stopped but his status is not refreshed and remain on pending. If you want to change Status you have to execute this script:
update ReportServer.dbo.Subscriptions
set LastStatus = ‘Done: 0 processed of 0 total; 0 errors (Stopped).’
where Description = ltrim(rtrim(SubcriptionName))