What are my rights?

We queried our account with Ekurhuleni and they admitted they had used the incorrect tariff when billing us for our electricity and this was happening for a number of years. They corrected our account and we received a credit on our account of over R60,000.00. Now my questions are:<br> Should they not refund us our money?<br> If not should we not receive interest for all this money?<br> It is going to take about 2 years to work off this balance with our monthly expenses.<br> What are my rights?