Call was billed incorrectly
'Wrong' rate was applied to the call
If you think that not correct rate was applied to the call, you should use Call Tracing to investigate such Calls.
Call was ANSWERED but billsec = 0
When Asterisk version >= 220.127.116.11:
Copy cdr.conf from /usr/src/mor/asterisk-conf/ folder to /etc/asterisk/ and restart Asterisk.
Call was ANSWERED but marked as UNKNOWN and not billed
If your Asterisk version is 18.104.22.168 you need to recompile core with such line:
#define AST_VER_14241 0
#define AST_VER_14241 1
Call duration does not match with Client/Provider
It can happen, if option "Media control – can reinvite/transfer" is set to "YES" on Device or Provider settings.
Why it is so?
Lets say that for some reasons client lost connection with internet. Usualy (when media goes through Asterisk), Asterisk would hangup such call because media is not received, but in the case of "can reinvite", Asterisk cannot see that connection is lost and it assumes that the call is active, while it is hanged up on client side. Than causes mismatching on billing.
Moreover, it is possible that Device/Provider is under the NAT. You need to check it with your Device/Provider and enable NAT=Yes (set NAT to "YES") if needed.