Well, firstly, don't think that just because you don't have a girlfriend at your age it means that you'll never ever get one because that's wrong. Girls at your age are probably more of a learning curve than anything and I believe I'm the same age as you as I'm doing the stage up from O levels too. What your dad's doing will pay out in the long run if you actually do study, but I agree that if he's telling you to do it constantly it's far too much.
Have you tried doing say maybe an hour or two studying and then asking to meet up? Maybe he'll see it as a reward for doing the work? As for the phone, what would happen if you just said you were texting friends? Does your dad have a reason for being this controlling?
Hope it all goes well