Dead Line for over a month!

I have been calling to complain about our work line that is continuously dead. Firstly waiting for an agent to pick up is a nightmare and when they do they have such attitudes on the call. As my line is a business line I was promised a service person would check the problem within 48 hours. It has been over a month with this problem. I have paid for services that have not been provided at all! This is shocking! Today after waiting for over half an hour for an agent to answer, she tells me over the phone that the technical department would have to call me and then further puts me on hold for a further 15 min until the call eventually cut. This is by far the worst experience I have had with a call centre and service provider!