We have lodged a service request with TPG to investigate why the planned outage stopped our internet service (i.e everything else seems to be ok: the link between us and TPG is up, the internet works when plugged straight in to the link, the firewall is ok, and the internal network is ok).
The last time this happened was October when we originally had the system set up and it took a day or two for TPG to fix. Hopefully then can just re-do what they did the last time.

UPDATE 6pm 28/7 the internet is working again.