PPP Session won't terminate

Hi.. I have problem with PPP connection to mikrotik. There are multiple L2TP and PPTP sessions that won’t terminate for days, even though the client has disconnected and change their IP addresses
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interface.JPG
I had to reboot the router to remove them, and put them on preset interface. Is there any way to let connection ALWAYS connect at designated interface instead of creating duplicates? I have put user name to the interface, and it worked first. But after disconnects, it created new interfaces.

Thank you