iPhone 4s goes to voicemail and does not ring

I apologies if this as been posted before. My iPhone 4s as just gone out of warranty and guess what an issue. When someone calls me it does not ring and goes straight to voicemail, i have tried

re-booting

Reset all settings

Reset network settings

switched 3G off

switched mobile data off

turned wi-fi off

turned bluetooth off

And its still the same, been in touch with my provider they do not want to know

I have recently been made redundant and relying on my phone for job interviews so i am desperate for a fix...help!!!!