Are you using caster sugar?
You need to cream the butter and sugar until it goes paler in colour, then beat in the eggs a bit at a time.
Sieve the flour then fold into the mix a couple of spoons at a time using a large metal spoon.
If using vanilla add at the same time as the eggs.
So basically you put as much air in as possible during the first 2 steps, then keep the air in when you fold in the flour.
They should be cooked in 15 minutes.
Buns should be 200, whereas cakes 180 for 25-30 minutes.
Let them cool for a few minutes before lifting them out to cool on a cooling rack.
They are cooked when you press down on the top and it springs back.
Don't open the oven door while they are cooking. Do 10 minutes, then just peek to see how brown they are.
The only time I have had flat buns was when I used a cupcake recipe which had milk in. They rose and the collapsed
but they tasted ok