You could make use of the Automations in Freshservice. Using automation like Supervisor, you could send an email to an Agent or a Group if a certain condition is met.
An example would be to setup a supervisor rule(under Admin-->Supervisor-->New Rule) with
Condition : "Hours since first response due/overdue greater than" (depending on your use-case)
Action : "Send Email to Agent" add the name of the agent to whom you would like to escalate.