WA Survey Strata with no common walls

[TQQ]

I recently purchased a new home on a survey strata lot. I have the original homestead and it was subdivided with two extra units built at the back of the property. The two units share a common wall and access their property from a rear lane way (no shared drive way). There is a common pathway running up each side so they can access a mail box at the front of my property. We do not have a strata company or any form of strata management. One of the owners from the rear unit recently took out a strata insurance policy covering all 3 of us owners for Strata insurance (which is only building insurance) and sent me a bill for 1/3 of it. I was of the understanding there is no requirement for this, especially considering we have no shared walls or common areas (the pathway is an easement on my property). I have my own individual home and contents insurance policy and thought this is the only requirement. Any info or help would be greatly appreciated. (It was subdivided in 1992 in WA, I hold 236 sqM and the two units hold 136sqM each)