Your story looks strange, because all Paris-Bucharest flights are AF operated (or Tarom...).
Some seats are sold under the DL or CO code, only in conjunction with a transatlantic flight (CO & DL do not have the traffic rights).
In other terms, you can get a CO code Paris-Bucharest only with a CO code transatlantic flight.
Is this the case?
If not, your travel agent broke the rules, under his own responsibility.