@Kristi16, if you etend a stay, one side has to send an alteration request and the other side has to accept it. Best is, you send the request with the guest beside you, check if the number of days is changed and if the price changed as well. If it did not, change the price manually, then send and have the guest confrim it immediately on their phone.
If you did not do that, you could just send a resolution request after you realise it and then it's up to the guest to confirm or refuse. If they are already gone, refuse the request and you do not have the discussion in the thread, you have low chances to get this money.
I hope this helps. If I misunderstood and you did not get paid even though you changed the reservation, that would not be good.