Deactivate of number without warning

Cell C cancel my cellphone number for not being active for 6 months. I use my number for my banking, receiving calls, sms and alarm system , on a daily basis. When i phoned customer service, they tell me my line was inactive for 6 months, if you don't buy airtime , receive calls, sms, in 6 months they deactivate the number. I told her i use the number on a regular basis, I just did not buy airtime for 6 months but that number is active , they could not tell me when was the last time I receive a call, or sms,. They just cancel the number without any notification. I just want to warn everybody , if you don't buy airtime on Cell C , they cancel your number and they don't you a chance to get it back. Never use Cell c again.