I shopped at tesco on 27th July but my account has been charged twice, what should I do to get my money back, it was 59.42£.
One is likely a pending authorisation.
Explain it to monzo and ask them to check (one transaction likely says pending at the very bottom), it should naturally release within 7 days.
But may be up to 30 days.
Monzo can see when the reversal date is.