Originally Posted by veloziROTHTOR
and then write back saying it's a breach of contract ...
How's it a breach of contract if it's a new tax (if I read it correctly), just assessed retroactively? Do you argue in a store that the marked price is $1.99 but you have to somehow pay $2.xx?
To OP, my advice would be to contact the landlord and offer to split the amount 50/50. Argue that if you were renting just now, they'd have hard time collecting from someone who isn't using the space now but was in 2011, but you also understand that your current rate is below the market (it is, right?), and you appreciate it. Bottom line, it's usually better to avoid conflict.