I don't live in the area now, but there used to be a 'latchkey' dog called Charlie matching the description (same area, same size and colour, same bone tag with name and number on it). The owners used to just let him roam the streets, usually around Strathcona, Imperial Avenue and Penkett Road, but sometimes in Earlston Park too. He would jump on and 'harass' my dog, then run off somewhere in the park. Like you I could never get hold of him to call the police. This went on periodically for weeks, if not months.
Once, when with my young niece he followed us and nearly ended up under the wheels of a van, literally 2 inches from death. So I followed him home to Carrington Road where the neighbours all seemed to know him. I narrowed down the house and approached the female owner who claimed he 'just ran off when she was getting the shopping in'. It seems that he must have 'run off' every day (or rather she couldn't be bothered to walk him and let him roam the streets by himself). She certainly wasn't bothered, or out looking for him, like I would have been if my dog had run off. And her daughter was playing with him in the street as if it was normal that he would be out on his own. I told her that I would phone the police next time I saw him out by himself and I didn't see him again, then I moved out of the area.
I kind of hope that this isn't the same dog, because this was two years ago, but it does unfortunately sound exactly like him