Appealing a CF83 Decision?

A relative has just been told she needs to pay Class 3 NICs following the assessment of her CF83. We've checked closely and believe she fits every Class 2 eligibility criteria with 8 years of Nat Ins paid in the 1990s having been ordinarily employed in UK immediately prior to leaving and then continuous work abroad since then paying EU social insurance (evidence provided to International CaseWorker) What steps can she take to appeal this decision? Is a Mandatory Reconsideration possible?

Hi Johnny King,
If you do not agree with the decision that our International Team have made regarding the correct class of voluntary National Insurance contributions that may be paid your relative may wish to send us a letter to ask that they review their decision.
If your relative could just confirm their employment details again then this would be helpful.  
Thank you.