I’ve been looking for this movie for a while, it was in colour, live action, and might have been dubbed into English. The main character was like the Pied Piper but played the guitar. The song I remember had the refrain “They’re gonna pay”. The movie is not the 1957 film with Van Johnson, the 1972 version starring Donovan, or the animated film “The Electric Piper”. Thanks!
A Happening in Hamelin (1961)
https://www.imdb.com/title/tt0061743/
Solved! Thanks so much, this has bothered me for years!
Marking “solved.”