Vodacom deactivate number despite credit

I went overseas in April 2017. Activated Roamon and managed to use the service for two months. Suddenly it stopped. I mailed Vodacom , a communications company, numerous times but they did not communicate or respond. On my return in March 2018 not being able to use my phone a learned from Vodacom that they deactivated my number for not using it. With Roamon not working I could not. Despite this I have a credit on my account. My wife on the other hand left her phone at home and her's is working. How can Vodacom deactivate my number for not using it, while their service does not allow me to use it.