I would probably contact the financial controller bird, but she will expect you to undercut her current cleaner or offer different frequency's that save's them money, someone has already posted what is involved so up to you if you can do it for a price you would be happy with, and a moral dilemma on whether you want to undercut or not, not that it would bother me 
We were always taught when 'prospecting' (looking for customers) that the first exploritory phone call must be to find the decision maker. So my first call would be the find out from the receptionist who the right person to speak to is. I would think that it would be Steve Young and conjunction with his two site maintenance men, Ted & Steve.
You have to win their approval before anything will happen.
We used to refer to the receptionist as the gatekeeper, as she has the power to block your entry any further. So you start by introducing yourself and ask for the name of the person responsible for clean windows
to update your records. (They can't say they don't give that information out over the phone as they have it all over their website.) You may have to prod for an answer, ie would that still be Steve Young's responsibility?
Once you have got the persons name, the receptionist may be happy to put you straight through, although most start to make 'excuses' or finding objections for not doing so.
In that case we put the prospect on hold for a day or so and phoned back once this call had gone cold in the receptionist's mind. "Hi, this is Tosh from the window cleaners. Please may I speak to ................." If you start giving her the name of your company/business you start opening up a hornets nest. (It is easier to say Tosh from the Garage, than to say Tosh from Reg Vardy BMW Croydon, Feet Sales dept.)
She will know that they have a window cleaning service and will most likely relate to or you being associated with their existing service provider.
Once you get through to the responsible person, your next objective is to get a face to face appointment with him/them. But you also need some information. Do they still have an outside cleaner dedicated to cleaning the windows; do they have a contract term, etc. (You already know now that they used to have a cleaner and how long it took a couple of cleaners from this thread). This will help you to decide how to procede.
You still need that face to face meeting, but if the cleaners have an annual contact that still has 8 months left, then it no use you pricing up for the job just yet.
You also need to leave a 'hook' behind to hang your hat up on for later. It's something you've got that no one else has so they won't forget you. You can refer to your Geordie/Japanese heritage - ie they must remember you as the Welsh Geordie Jap (not chap - get it?).
The accountant is only any good for paying the bills, but the first point of call with regards to payment follow up will be your original contact IMHO. (In the motor trade is was important to get accountant approval when getting new capital equipment as they could very easily veto a purchase. So they needed to be included as part of the decision making process.)
Good business exercise.
Spruce