The best thing to do is fill out a billing support request to determine what pricing those fall under.
You can investigate items that incur billing charges by enabling the "Usage" Diagnostic setting Category. Calling has additional information available through the "CallSummary/CallDiagnostic" diagnostic settings along with an associated workbook that will detail for each call the duration/end/reason for each participant. These settings will have to be enabled prior to the call starting. See Call Summary and Call Diagnostic Logs Preview for more information about the calling logs.