How do I activate landline service?

Hi: I'm a new customer, and I just had a modem installed yesterday. However, there is no dial tone on my landline phone: I have tried everything I can think of, but to no success. I chatted  with an agent, and they told me I had to activate my service by phone.

Unfortunately, the contact number they gave me is not available in my area (06355); what number should I call instead?  Or is there another way to activate my phone service? Please help.