I deleted an extension but it still is able to register and make calls. I restarted a couple of times but bug still persists.
Which extension no? Did you try to re-create and delete it again?
116 Didn't recreate the extension.
We looked into your System Log. There are no successful registrations of extension 116. Instead it constantly repeats: Feb 15 13:54:19 NOTICE[112489] chan_sip.c: Registration from '"alexcheam-116" <sip:alexcheam-116@sip.pbxes.com>' failed - Username/auth name mismatch Please re-check.