<?= date('d.m', strtotime('13 week last Monday')).' - '.date('d.m' , strtotime('13 week Sunday')) ?>
$date_start = new DateTimeImmutable('13 week first monday of Jan this year - 1 week');
$date_end = $date_start->modify('+6 days');
echo $date_start->format('d.m') .' - '. $date_end->format('d.m');
// 26.03 - 01.04