Someone help me my dad never agrees to getting a new house and when we tell him he says if I can't get you a bigger house because this house is messy and I told him of course it will be messy of the house is small but he doesn't listen please help me

This is what your Dad may be thinking. If the people living here can't keep a small house clean, a larger house is just going to result in a larger mess.
That is exactly what I would be thinking.

The house is a mess because we don't know were to put our things from how small the house is and we have to put our winter clothes in the garage and then when its winter we want to wear them they have a little of mould :(

I obviously don't know your Dads reason for not moving into a larger house.
Perhaps that he cannot afford a bigger house, perhaps he is putting away money for other things the family needs, there is no way for me to know.
The bottom line is that your parents have the final say and if dad says no, then no it is.
Perhaps you could go through your clothes and donate some to Goodwill or The Salvation Army.
With fewer clothes you could maybe find the room to keep them all in your closet and dressers year round and not have to put them in the garage.

We moved into this very small two-bedroom house back in 1972. It was our "starter" home. The years went by and we never bought a bigger house. We weeded out old clothes and things we no longer used and kept the house neat inside and outside. We had two sons, one of whom still lives here. We've saved tons of money by not buying a bigger house, so we were able to pay for one son's college education and had money left over for retirement. This little house is now our retirement home.

Like LadySam said, maybe your dad has plans for the money he saves by not buying a bigger house. Maybe that money will put you through college or be your wedding present so you can buy a house with your new husband.

Perhaps your dad can't afford a larger house and does not want to admit it to you.

But he is right, there is no excuse for a messy house, small or large, things are put away and stored.

And sorry many people put winter or summer clothes away in garage, or attic or somewhere and there is no reason for mold. That is a issue on how you are storing them.