First I’ll assume you did not have a plan with Southern for some fixed term whereby the only way to prematurely end it will be in the plan T&C, and something may have gotten missed but they remain unhelpful to clear it up?
Are you only receiving bills or have they been taking direct debits? If taking direct debits see these other topics that include links to resources as well as rules. Note it is a different process to stop direct debits for a bank debit vs a credit card debit.
You seem a very patient person. I suspect most in your situation would have done that months ago. Please keep your topic updated as your experience and eventual path to resolution may help others who find themselves in a similar predicament.
AGL is not known for their administrative competency (to be kind) and this problem suggests they may have trained Southern Phone.
