Welcome to the forum, you might want to have a look at the following FAQ which explains where everything is
Welcome to Benefits and Work Yes, it's a waste of Tax Payers money to reassess someone so close to retirement but unless the requirement is removed by the DWP then you have no choice but to attend.
Is this the first appointment? If it is then you can cancel, this will push the appointment back at least a week and possibly a lot more.
You could then ask for the assessment to be recorded, this usually results in the appointment being re-arranged at no fault to you.
With luck, you might make it to retirement without a Decision being made.
Gordon