Thanks for the prompt response and for drawing my attention to the “anonymous” line.
At that line I noticed that it is not only anonymous but “PJSIP/anonymous”.
Using this information I managed to resolve the problem.
Initially, I defined the extensions as CHAN_SIP and on the CSipSimple application I defined the account to use it’s respective port (5160), but as the log shows it is using PJSIP.
To fix the problem, I changed the extension to be PJSIP type and the port on the CSipSimple to be 5060.