Aside from moving and complaining to the landlord and whatever local agency is appropriate, the answer is nothing. Well...you could stop paying rent, but that would likely get you evicted, which gets us back to moving as an option.
LOL! Of course an email is "in writing" - both colloquially and legally. Are you suggesting that email is a means of verbal communication?
I continue to be baffled by folks' obsession with certified mail.