[mothered]

I have said all of this in an email to them now, waiting for their response, if they don't budge, I will try to find a managers email address or something to email instead

Wait for their response and If need be, we'll tackle the next step from there.

as I have been stuck with a really stubborn CS rep, who said I can't escalate as they are the team leader.

Nonsense.

The rep Is not part of senior management, nor the escalation team - who specifically handle complaints of this nature.