Mango fails to communicate

I had flight ticket booked for 21 September, and couldn’t make it. I phoned on the 20th at 18:30 and spoke to Laetitia, as I couldn’t change the ticket online, and there was no payment option for the difference. She assured me it’s been changed to the 7th of Feb 2020, and I won’t have to pay a fee. Up to today I still haven’t received any confirmation, flight number etc.