That's outrageous Steve! And you were only seven?! Do you think nowadays the dog would be put down by the authorities for its second attack?
And putting poo through your mum's letterbox!! Disgusting!
The thing is, dogs need a lot of exercise and some owners don't provide it. I reckon this makes the dogs bored, edgy and vicious. It's cruel to the dogs, and ignorant on the part of the owners.

When we cleaned a holiday barn out near the North Norfolk coast, we often had 'guests' with dogs. A maximum of three dogs was allowed. When we arrived, often the 'guests' were just packing up to leave. But when we pointed out they should pick up any dog poo in the barn grounds they usually kicked off. They seemed to think that was our job! And as often as not, they'd showered their huge dogs in the bathrooms, using the white fluffy bath towels we provided to dry the animals with. And the dog hairs! On everything! It made our work twice as onerous.
Our neighbour is the 'groundsman' there still, he has to cut the grass and sweep the patio etc, and he never holds back. I've heard him tell some 'guests', "Dew yew git orl that shit clared up orf the graaaass afore yew goo. Snot moi jarb! Them dawgs is narthing but Bloody Shit Machines!"