Have you already submitted an application through UCAS? If not, then this is what you need to do, if you want to use clearing effectively to contact more than one institution.
Many lecturers and admin staff go on holiday at this time of year and return in time for the release of A level results, so responses slow down. Try calling the admission tutor directly, if you need answers. If they are not there, try the main switchboard and ask to be put through the department administrator. Usually one person is in the office and may be able to answer general quesitions. For the popular courses, they may not know if there will be any clearing places until the A level results come out.