So if I pay £312 every month for 20 years I end up paying £74880, but I still owe £75k, and I don't own the house/flat I live in right?

But if I do it on a capital repayment mortgage, and pay £438 a month for 25years (300 months) I end up owning my house/flat totally, but I will have paid £131400 for a house only worth £75k.....????

Neither of those make any sense

I don't get it - people say you can make money from houses, but if your paying £131k for a house you can only sell for £75k, surely you LOSE money?