Cell C contract cancellation impossible

My husband has been trying for three months to convert his cell c contract to pre-paid. He has had the number for over 15 years. He "fails" the verification test. How on earth is a person supposed to remember what Cell C has on file and for which period they are asking the questions. We have had 6 addresses in the past 7 years alone!. They did not even have his email address. They had a Standardbank payment address on his profile., where they get this only they will know. We updated the profile and gave that info and they still say it is incorrect. Cell C branches are also unable to assist ????? This is absolutely pathetic service from Cell C. It is very easy to take out a contract, but heaven forbid you no longer want to make use of their services.