Troll Stinks!, Paperback/Jeanne Willis

Billy Goat and his best friend Cyril are messing about with the farmer's mobile phone, taking selfies and playing games... until they discover the number for a troll. Grandpa Gruff says all trolls are bad, so Billy and Cyril decide to get their own back by sending mean messages. After all, trolls really do stink! Don't they?