Yes, you can purchase your item in multiple sizes, but there are some rules you must follow in order to protect yourself from getting banned on the desired website.
For example, if you want 3 sizes, you must create 3 accounts and each account must have a different payment method with different cards.
On your billing info you have to change some stuff in the address, for example:
Street -> St. -> Strt.
Avenue -> Av. -> Avuene
If you have any questions or doubts about this, feel free to contact us to firstname.lastname@example.org.