Bought a property because of the cheap property tax, now 2 weeks before closing it turns out it was incorrect and is 102% more than originally stated

This is for my FIL. In/Around Hamilton, ON.

He bought a property recently and the closing date is in about 2 weeks time.

One of the biggest reasons for his purchase was the stated property tax rate, which was advertised as being $1834 in 2024. He is buying the property without a mortgage and liked the cheap property tax.

However, after the lawyer got back to us with official documents, it turns out the 2024 property tax rate was actually $3715, 2025 was $39xx and 2026 will be $4266.

For the 2024 rate, this is something like 102% more than what was advertised. Over 10 years this could cost him nearly $20,000 in expenses he didn't plan for.

Besides that, my FIL asked multiple times if the stated property tax was correct, and the realtor responded saying that while the 2026 rate wasn't published, it was indeed around $1800-2000~ for 2025. We have this in text messages.

My FIL didn't have a real estate agent, however the seller's agent offered to represent both sides and he agreed to it.

What are our options here? Could the purchase be voided due to misrepresentation? Could we ask for compensation? Not sure what is typical in situations like this.