Q: Somone else is using my Apple ID to buy things

I've had several emails from Apple showing an invoice for various amounts of money saying that I have subscribed to Apple music or bought some app from the app store when I haven't! I've changed my password several times and it keeps happening, although no money is being withdrawn from my account, I think I've hacked!!! doe anyone know how I can stop this from happening because Apple Support is useless!