My phone is not receiving calls.

Hi

My phone is not receiving calls. I can make calls and texts but everytime someone tries to call me they get the engaged signal.

What is wrong with my phone?

Thanks

Jane

My sons motorola 3rd generation phone is not receiving calls. I can make calls and texts but everytime someone tries to call me they get the engaged signal.

Also my daughter's phone which is the same make and model cannot make calls, receive calls or texts.

Please help. They have done nothing wrong. Has there been some kind of a software update that they do not know about?

thanks

Jane