There is no provision in the T&Cs for early termination due to coverage issues.
Have you reported your issues to EE to allow further investigation? There may have been some alterations to the network in your area that have caused this, but sometimes one of the means used to measure the success of changes, is customer complaint volumes and/or fault tickets raised in the immediate aftermath.
I'm not sure of the context of your second question, but "install new network sites" is how a network would often refer to the installation of new radio sites to provide additional coverage and/or capacity.
