Mondo and Mtn are *****s

Bought a iPhone 16 on Mondo via Mtn and they delivered iPhone 15, they said i can cancel the contract before 10 days and it would take about 21 days to cancel, 21 days pasted and now they are telling me there was a delay on their side while canceling and they are going to debit money at the end of the month and i must wait another 21 days for them to refund me