The certificate of title of the strata is the sole document advising lot property boundaries and common property.
You are trying to claim adverse possession, a form of squatting. Unfortunately adverse possession requires more than just using common property.
In a perfect world Your conveyancer should have pointed out the illegal use of common property. The reality is that conveyancers don’t physically inspect the property in order to compare the title deeds with reality.
When I purchased my first strata property, my solicitor places the strata plan in front of me and asked “show me what you think you are buying”. Great way to find out if what I was shown was on the plan.
As in all commercial transactions, never rely on the word of the vendor unless they are prepared to include it in the contract.
Sorry, you are out of luck.