I googled managing agents.. and came up with these people
http://www.arma.org.uk/ Association of Residential Managing Agents

However, i imagine that the managing agents concerned would need to be members to be able to get anything done. But it might be worth geting in touch to see if they can offer any advice.

I'm not sure what your problem is, but i can certainly empathise as I am in the process of moving and having a painful time with the letting agents. grrrrrrrrr

good luck