Perfact, When you try to use DB in Single user mode or readonly mode It will not allowe you to do that, because some processes still using the DB and while DB in use then you should not be able to do any one of the options.

If it is an urgent scnerio then probably you may need to kill the processes from the QA by using SP_WHO2 ACTIVE

Make sure you can not delete any system process or self process as well.