Which internet providers service the Seaforth area?

You are limited to Optus and Telstra. Telstra is the only Cable provider and Optus is limited to ADSL 2. The internet connectivity in Seaforth is limited by the age of the Telstra copper network and an ancient Telstra telephone exchange at Balgowlah. The exchange regularly undergoes upgrades but it seems to me its beyond meeting the demands of the digital age and will have to be replaced in the near term.
Internet outages are all too frequent especially after electrical storms.