Dowie's right, the prozzies must have gotten their details from somewhere, how about asking them how and when?
Not trying to be Sherlock here, but who do they know that:
- knows where they live,
- knows their mobile number,
- knows the name of their partner,
- has a link with Canada,
- has a grudge against them
Perhaps get a new mobile number and slowly give it out to certain people, when the abuse comes through on that line then they may have a likely suspect.