Cheap flights from London Gatwick Airport to São Miguel from £79

First we did not get to sit in the seats that I paid for and selected months prior to departure. We were a party of 4 family members all with aisle seats. Agents told us there was nothing they could do flight was full and they couldn’t change anything. Plane was delayed leaving Barcelona. Made our connection to next flight very tight. We had to run from Gate 22 to 44 with no assistance other than employees yelling at us along the way this way to Boston. There were 40 people doing this of all ages. We had our correct seats that I paid for and selected for the next leg of the trip Lisbon to Boston but when we finally got to the gate from running the gate agents changed our boarding passes after saying she wasn’t changing anything and put us in seats that were unacceptable for a 7 hour transatlantic flight. What was the purpose of me paying for seats beforehand for them not to be honored? Again the 4 of us all had aisle seats but ended up with my husband and I sitting in a middle and window seat. My sister in a window seat and my brother had an aisle but not the exit row he requested due to his height and size. I want a refund of my expenses for seat purchases not honored on either leg of the flight.