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These are two different sentences and unrelated to each other.
First:
REISSUES/EXCHANGES NOT ALLOWED TO EOU/ERU FARE TYPES.
These two fare types are basic economy. This means your ticket cannot be exchanged to a basic economy fare. If your ticket already is a basic economy ticket, then perhaps your travel agent's strange interpretation would make some sense. But otherwise it doesn't.
Second:
AFTER DEPARTURE CHARGE USD 275.00/CAD 275.00.
This means that after you begin your journey, changing the ticket will cost $275 (plus any difference in fare).