Hi Zee.
I’m really sorry to hear how you’ve been scammed like this.
From history on here, Monzo does seem to return the money to you, if you can show you genuinely believed you were talking to Monzo.
Write a timeline of everything that happened. Use your call logs/texts for the times.
10:05 - Outgoing call to Monzo
10:19 - Incoming call from 0…
10:42 - Text message
etc etc.
15 days is industry standard and you’ve done the best thing you can by reporting it quickly.
Have a look here for people going through the same thing;
Try not to blame yourself for it. These scams are incredibly sophisticated these days and they make themselves very believable.