10 Year old business with a vodamail email is no longer working

For about 10 years we have been using the email address: ********** for our electrical company. Last week it randomly asked me to renter my email address password after almost 5 years. After 5 years and not remembering my password, I simply navigated to the forgot password link. It then said that they would send an OTP to my email address cellphone number sim card ( ********** 811), since 2011 we have been using ADSL wifi and thus no longer used the Vodacom 3g ****le. We have lost the original email address sim-card (5 years later). So the next step was to go to Vodacom to get a sim swop in order to be able to receive the OTP pin in order to reset my email address password. The staff then said that the cell phone number was not used for over 3 months and therefore the number has been deleted and we can no longer receive a sim swop for that cellphone number thus not being able to reset out email address password. So what does this mean? We have been running and using this email address for over 10 years and have built customer relations through this email. What would be the next step to retrieving my email password? It would be absolutely horrific if there was no way to reset my password