Triple Net Lease

I have been in a building for 20 years. First 8 years I had a straight lease. Just paid $1000 a month that included everything but electric. Then a new individual bought the building and changed the lease to TRIPLE NET. I have to pay rent, and my percentage of taxes, and building insurance and common area snowplowing and the such. About 4 years ago, they triple net lease expired and we have been paying just month to month and paying the real-estate taxes and insurance. We have been paying 20% of all the real-estate taxes and insurance as we thought we had 20% of the space in the entire building.
Now it has come to our attention, we only have 9% of the entire building, so we have in essence over the last 10 years paid over $10,000 EXTRA of our share of taxes and insurance.
The million dollar question is, doe TRIPLE NET LEASES specifically state in MA that you only pay a percentage of what you lease, or can the landlord say you pay 20% no matter what amount of space you rent? We do not have copies of the original lease, nor will the landlord give us a copy since we have been paying month to month. What is our legal rights?