I had the same experience before when I got a new number from Bell. I normally got 4 to 5 calls every day, sometimes in the mid of night. I complained to Bell several times and used every possible function they suggested, i.e. block, trace, etc. no use at all, the calling no. were always changing from different places, all were fax signals. I finally got no choice and complained seriously to Bell and insisted I need another no. as this no. must be a fax no. used previously and there are a lot of companies had programmed fax sending in automatically.
Stupid Bell always wants to sell their services instead of solving the problem for you. Be strong when you complain and tell them you can't stand anymore, either change the tel. no or change the co. (you have other choice now), they should be able to give you a new no. That's the only way to solve the problem completely.
Yes, Bell should offer you a new tel. no free of charge. That's what I got. It's their responsibility, actually we should ask them for reimbursement of the disturbance, shall we?
If they don't care you very much, tell them you want to speak to their manager who can solve the problem completely for you, be strong enough, it's my experience.