How long were the segments (green oval stems)? In Opuntia stricta they are usually less than 20 cm long, and in ficus-indica they are usually more than 30 cm long.
"Weeds of the South East' describes both O. ficus-indica and O. stricta as "usually spineless". This looks like O. puberula http://canberra.naturemapr.org/Community/Sightings/Details/1973900 but I am no expert.
I had not checked puberula, which is in the ACT but not NSW, so not in PlantNet, but it is in Vicflora. Puberula, despite its name, is not hairy, bue covered in fine warts. I can see no evidence of thses in the photos, but I suspect you would need a macro to pick them up. Stricta has segments less than 20 cm long, 0-11 spines per areole, spines 10-50 mm long. Ficus-indica has segments 25-50 cm long, usually spineless, but can have up to 9 spines per areole, about 4 mm long. Puberula has segments 9-22 cm long, 0-3 spines per areole, spines 5-17 mm long. Please comment, Floramaya.
I have confirmed this as Optunia puberula (Opuntia sp. in NSW plantnet) on the basis that segments seem to be small and less than 12cm, the areoles are close and arranged in diagonal lines, the whole plant seems small and not much above 50cm and it is pretty spiny.