When you receive a summons for a lawsuit, how can the plaintiff be listed as the original
Creditor, when they charged the account off and it has been with three other debt collectors since, now it has been taken by Mann Bracken LLC?

Charge off is an accounting term having nothing to do with not being due the money. Those 3 different debt collectors may or may not have 'bought' the debt, rather have been hired to collect the original, which is seems is the case with this final collection company.