Complex sentence: Griffiths was not invited to McCartney's house for the next rehearsal and when he coincidentally phoned them during the practice session, drummer Colin Hanton had to let him know he was no longer in the band.
Split into simpler sentences: Griffiths was not invited to McCartney's house for the next rehearsal. When he coincidentally phoned them during the practice session, Colin Hanton had to let him know he was no longer in the band.