Can you buy real estate with a notarised power of attorney without my knowledge?

No. When buying property with a notarised power of attorney, the seller must of course be paid. Even if we have a power of attorney, we do not have access to your Belgian or Dutch bank account with a power of attorney.

Buying a property with your power of attorney in someone else's name is also not possible.

By the way, using a notarised power of attorney without your consent is a criminal offence.