Did you mention in your email that you have a hard deadline on a funded offer? When I applied--under analogous circumstances--Oxford was willing to give me an early response. That was in law, not English (though they're in the same building, funnily enough), but I would be shocked if they were not willing to accommodate you.
It may be that they simply haven't completed their selection process, in which case nothing can be done for the time being. But the internal deadlines for departments (i.e. the time at which selection committees have to send their list of offers to the administration) are usually very close to March 15th (a bit before or a bit after, not sure for this year), so the department should have made its decision before then.