Two large stones were thrown through the window of their house at Rockview Park in what they say is the thirteenth time they've been attacked since June.The couple, who have five children - the youngest aged just five months old, have lived in this part of Co Londonderry for two years but have told UTV they now plan to leave.They said: "We are very frightened and we don't want to live here. We're frightened to sleep because we don't know what's going to happen and we're frightened to go out."In the latest attack, which took place just before 11pm on Tuesday, a piece of concrete was thrown at the front window smashing the outer panel and double glazing.Police are treating it as a hate crime.The family continued: "We've lived here for two years and this is the worst incident. Since June there have been 13 incidents, attacks on our car. I think it's because we're from Poland."Anyone with more information has been asked to contact the PSNI.