When did you make the booking and did you have 50,000 in your account at that time?

If you did not have the points at the time of booking, the price that they will charge is the price per points when you have the points in your account (aka dynamic pricing). The current price is 60K, this is what you are going to be charged. It is not relevant what was the point price at the time of booking, because you did not pay it at that time.