Hi, I have a billing question. I was billed 10000 contacts but I deleted some of the contacts so it is around 6000 contacts. Does anyone know why this happens?

Can I delete the contacts and stay under few contacts and get billed less? ( I don’t contact the customers 1:1 and only use dm automation. So I don’t need contacts)

If I can't, the price will skyrocket as my business goes on. 

Thank you for reading this, and appreciate your responses!