With Scootaloo adopted there was just one thing left for her orphanage to do. It was a rule there that they would let a parent know when their child had been adopted. That way they would know whether or not the child was still in the orphanage and, should they so choose later down the line, re-establish contact. In very rare cases a parent was not informed. This usually happened when a parent was abusive and a child was taken away for their own good. If Diamond Tiara had ended up in the orphanage then Filthy wouldn't have found out when she was adopted. Luckily for him he was there when Firefly offered to take Diamond Tiara with him so it wasn't very hard for him to find her again. Her ending up quite successful had helped there too.
Unluckily for Scootaloo the abuse of her father was never reported. As far as the orphanage were concerned, her parents had given her away because they couldn't cope with her. This meant that when she was adopted her father would be informed. Her mother had long since passed but her father was alive and well. Well, drunk anyway. He had also left Canterlot quite a while ago. He had ended up in quite a lot of trouble with the law in his new home but none of it had really reached Canterlot. The orphanage had no clue. So they had no choice but to send him a letter.
When Scootaloo's dad opened the letter he read it while mumbling to himself. His voice was grizzled from all the abuse his body had been put through over time. "Blah blah blah....Canterlot Orphanage....blah blah blah Scootaloo....blah blah blah adopted...wait what?" he all but roared when he read it. He had to read it several times to make sure it really had said that Scootaloo was alive and well and even adopted. There was no mistake. "Ponyville eh? I guess my little girl is about to have a visit from her dear old dad..." he said to himself. He smiled to himself as he thought of what he could do to Scootaloo. He had helped bring her into this world and in return she had ruined his life.
Now it was time for him to ruin hers. To get the revenge he never thought he'd be able to get.