Hi Mum of 2 monkeys! I really feel for you as we initially had terrible problems trying to get our deposit back from our landlady which she had no right to keep. As she & Foxtons were awful throughout our 3 year tenancy I was expecting there to problems when we moved out so had kept absolutely every email & note written, which did help us in disputing the return of our deposit. We used the government backed
http://www.mydeposits.co.uk/ who were really good. You speak to helpful native English speaking people on their phone line & then should you want to register with them to sort out your dispute it is free & very simple. We got virtually all our deposit back (except for the cost of replacing 2 door handles which were not working when we moved in, but because I hadn't complained about them & asked for them to be fixed I had no evidence that they were not working prior to our tenancy).
Another word of advice, if it is not too late (as it was for us): unless your inventory states that the house has been 'professionally cleaned' you are under no obligation to pay for professional cleaners when you move out (Our inventory did not state professionally cleaned & Foxtons charged us just under £400 for their so called professional clean, that turned out to be simply one woman & a mop for 3 hours!)