As Twix123 indicates, you shouldn't be paying National Insurance Contributions but you might need to obtain an Age Exception Certificate to prevent them being deducted by an employer.
As Chris says, you'd need to obtain the Age Exception Certificate, this has to be given to your employer as their formal authority NOT to deduct NI from your wages. Although they will know you are over 65, they have to keep deducting it until they have that certificate on your pay records.
You should stop paying NI after you've reached State Pension age, so bearing in mind that is going up, then some people(and in time most people) will pay NI after age 65 on any wages they earn.
Also bear in mind that NI is not payable on any pension income you may have.