A relative of mine parents have been contact by phone claiming to be from Ancestry asking questions
When you say "claiming to be from Ancestry" - do you mean someone who works FOR Ancestry, or someone who said they have a tree or an account with Ancestry or a DNA test via Ancestry? Were they asking personal questions about your shared family? Did the person who called them have a particular accent, or say anything about themselves - or indicate what their objective was?
and also received an email claiming to be from me.
Unless your email account has been hacked, I don't quite understand this - was the email actually a message sent to your relative's parents via email but generated via a messaging forum and had your name on it? If they were to reply to what they received - what reply address comes up?
It certainly all sounds very fishy, and must be very unsettling for you - but from what you say, I'm not convinced it's an Ancestry security breach. The contacting of yourself by the Australian lady initially, seems all above board - Private trees can be still appear on Ancersty searches with minimal info, enough to reveal a possible connection and Ancestry then suggests the searcher message the Private Tree owner.
Hopefully Rootschatters with more knowledge in these things will be able to help more.
Cheers
AMBLY