Non-ringing problem

I have 4 numbers with cellc. I keep getting phoned from cellc to renew the contract of 2 of them. I refuse. It is those 2 numbers that are causing problems. The problem is that when I phone someone with either of those 2 numbers then 80% of the time the phone does not ring - it is dead silent and nothing happens. I can't phone cellc customer care because guess what - their line doesn't ring either. If this continues I'm cancelling all my numbers with cellc