[Paris]

My name is Paris, my flight was on Jan 04th at 09:00AM from FRA to DFW. And, I was suppose to be back in Dallas on Jan 4th 08:19pm. However, my CDG to ORD flight is canceled with maintenance problems. First we waited in the aircraft about 2 hours, they said the aircraft has some issues and engineers were working on it while we are in aircraft. Then we took off after an hour later Pilot announced that he didnt feel safe to fly, so we had to go back to Paris, First of all if the aircraft not fixed how come they let us fly? It is a big safety issue! For God sake noting happened and we landed back to Paris. Then, I am rescheduled for Jan 05th at 1pm. In the morning of Jan 5th, I am told that my flight has been delayed to 05:00pm and, I was not going to be able to make my ORD to DFW flight either. When they told me that my ORD to DFW flight is rescheduled to Jan 6th 06:00am. I purchased another flight from American Airlines for ORD to DFW on Jan 5th 10:15pm (see attachment) It cost me $118. After all, my ORD flight is delayed again so i did not make my DFW flight on Jan 5th. Basically, I lost 37 hours because of lack of maintenance on united's old aircrafts! I missed 2 days of work and important meetings, probably it will cost me thousands of dollars!It was my first experience with United Airlines. As of Company, we always fly with Virgin America or American Airlines. And, we never had such an experience like this. After all that bad experience, they sent me with $500 travel certificate?(At least I was expecting a full refund) I would like to know my rights on this kind of situations and where to apply for a refund and cost for missing work days.