Just in case if someone stumbles onto this thread then here is a bullet proof solution to SQL Server stuck in SINGLE USER MODE
-- Get the process ID (spid) of the connection you need to kill
-- Replace 'DBName' with the actual name of the DB
SELECT sd.[name], sp.spid, sp.login_time, sp.loginame
FROM sysprocesses sp
INNER JOIN sysdatabases sd on sp.dbid = sd.dbid
WHERE sd.[name] = 'DBName'
As an alternative, you can also use the command “sp_who” to get the “spid” of the open connection:
-- Or use this SP instead
exec sp_who
-- Then Execute the following and replace the [spid] and [DBName] with correct values
KILL SpidToKillGoesHere
GO
SET DEADLOCK_PRIORITY HIGH
GO
ALTER DATABASE [DBName] SET MULTI_USER WITH ROLLBACK IMMEDIATE
GO