Unless your complaints have to do something specifically with the marketing of the flight (e.g. the trip was never successfully ticketed, stranding passengers abroad), complaints should go to the operating carrier.

If they had been downgraded on the entire trip (BOS-PHL-DUB, not just BOS-PHL), UA would refund them the price to the cheaper class of service, but that didn't happen here -- at least one flight was operated in the originally ticketed class of service. NOTE FOR FUTURE REFERENCE: if they had flown domestic F in one segment and international coach in the next segment on an intl J award, UA would not probably offer a mileage refund!