I booked 2 tickets using miles+cash last night. As soon as I completed the booking realized that I accidentally booked the wrong date. Called the number from OPs post got through to an agent in a few minutes. Was told that they can't fix my mistake, that I'd have to cancel and book a new ticket. Luckily I had more miles in my account not to have to worry about waiting for the re-deposit to appear.
Was placed on hold for a couple of minutes. Agent returned to tell me that I was speaking to Avianca and needed to call Taca. At least that's what it sounded like what she said. The number I was told to call was 800-400-8222
Called that number and again got through within minutes. Agent basically said only thing I can do was cancel. Among other things verified the exact amount that I paid in cash for the flight. I was never placed on any automated system to enter pin or CC details only things verified were date of birth, flight details and amount paid. Was told ticket would be cancelled within a few hours. I am no longer able to look up the PNR on LH.com while I was able to look it up shortly after booking along with etickets. I also see both a pending charge and pending refund for same amount on my credit card. I was never told anything about a cancellation fee and not sure how they would charge me for that now. Maybe I got lucky and won't get charged that fee.