Unless indebtedness approved by the voters, contracted, or incurred prior to the date of consolidation or annexation as provided herein has been assumed by the voters in the other city or cities in which such indebtedness did not originate, such indebtedness continues to be the obligation of the city in which it originated, and the legislative body of the consolidated or annexing city shall continue to levy the necessary taxes within the former city that incurred this indebtedness to amortize such indebtedness.