If the customer identifies payments wrongly duplicated within the transactions history it is probably for the reasons below :
Payment by card
Due to low signal, the payment terminal wrongly notifies the customer that the payment is declined while the card was correctly debited.
On this scenario, duplicates are automatically cancelled within the next hours. Authorized payments can remain pending for 10 days maximum and then cancelled automatically. Click here for more information.
Payments sent to other individuals
Due to low signal, the customer can lost the connection with the app during a payment process. It could lead the customer to perform a second transaction that will be considered as a duplicate.
On this scenario, it is necessary to follow the instructions explained on this article.