Extracting blood from an airline

I eventually got round to contacting BA again about my compensation claim. I again received a very prompt reply saying that they've reviewed my situation, and are very sorry and all about what happened, but they're "unable to increase our offer to you". Well currently what they are offering me by way of compensation is nothing, so suggesting that they can't make an increase on nothing is a rather bizarre way of saying that they don't think I deserve anything! I'm not sure whether to continue pursuing this or not, but they're continued line that they hope that this decision "will not deter you from flying with us in the future" gets more annoying.