BMI flight

Hey folks
I originally booked a return flight to LHR for the 1st sept (returning in november), but got the times messed up. So I had to book a new (earlier and one way) flight to LHR.
Since I won't be taking the flight I originally booked does this mean that the return ticket I booked from LHR will be invalid (as it is the same ref) or can I still take it ok?
Many thanks!
Kris
sorry forgot to add, the ticket was non-refundable and so had to buy a new one!
I originally booked a return flight to LHR for the 1st sept (returning in november), but got the times messed up. So I had to book a new (earlier and one way) flight to LHR.
Since I won't be taking the flight I originally booked does this mean that the return ticket I booked from LHR will be invalid (as it is the same ref) or can I still take it ok?
Many thanks!
Kris
sorry forgot to add, the ticket was non-refundable and so had to buy a new one!