it would be quite useful to be able to associate a third party ticket number with the call, (maybe under child tickets) so when talking to a provider for the second or third time about an issue that you have escalated to them you don't have to trawl through your stored e-Mails and notes to find their ticket number
Did you try configuring custom fields in Tickets for storing the third-party ticket numbers? More information can be found here - https://support.freshservice.com/support/solutions/articles/154126-customizing-ticket-fields
Let me know if this is useful.
Product @ Freshservice