What can I do if the unit can not be turned off with either the remote control or the on / off switch?
Please check the following:
Does the switch on the device work properly?
Are the batteries of the remote control correctly inserted and charged?
Is the receiver for the remote control possibly obscured?
If your device does not respond to the pressing of buttons you can remove the battery (if removable). If that does not help please let the battery run completely flat until the device turns off. If such behavior occurs continually then try resetting to factory settings as this will often resolve the issue.