Gosh, the other owners shouldn’t be ringing and harrassing you, that’s not on. Tell them to stop or you will contact the police. Anyway…
From what you have said the stairs were built as part of the original construction, and further plans weren’t required by Council. The important thing is, what is on the strata plan. Are the stairs marked on the strata plan registered with the Department of Lands as common property or as part of your lot? Or are they just not there? If you don’t have the registered plan go and get it.
I am not sure of the position if they are not on the plans registered with the DOL, but I am not so sure that the OC can say that they should be removed. If they have always been there, then they can’t suddenly demand that they be removed. Presuming they do not form part of your lot, even if they weren’t designated as common property I think they would be the responsibility of the OC, because in the absence of them being designated as being part of a lot, then they would likely form part of the common property. You also say that they had previously been fixed by the OC, which suggests that they are common property, or at least that the OC accepted that they are. If that is the case they can’t just change their mind because it is expensive.
Anyone else feel free to correct me.