Fax number move

Hi

One of our offices have moved we wanted to keep the same fax number but were advised we couldn't, assuming its on a different exchange?

So I asked Digital Mobile if we could keep the old number and get it forwarded to the new fax number but were advised that this couldn't be done and they could only forward faxes to a 3rd party fax service.

Is this really the case that what I asked cant be done?

Cheers