SIM permanently disabled without warning

My SIM card with the number that I've had, and used with Cell C for about 9 years, suddenly stopped working. When I phoned customer support, the response was that the SIM was permanently disabled, and that there was no way to recover the number. This was because I hadn't recharged airtime to the SIM in three months (Even though I still had a positive balance, and had been receiving multiple calls and messages) . This is a very hostile way to treat long time customers, as there is no warning before the SIM is disabled. Having lost a number I have had for a long time is a major inconvenience, and will most likely mean that I will no longer be a Cell C customer.