Mobile Application save data

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C#

ASP.NET

I had developed a mobile recharge application for this i got a third party API and i integrate this in to my application. now it is working fine and we are able to rechage the mobiles.when the data we send to API for rechage we just save at our end i.e. customerID, TransactionNo etc. in the sql server database. but we are thinking that we can reduce the time which is taken when the data is saved in database. can anyone suggest me how can i reduce the time while saving data in database so that we can give the quick response to the customer and it does not create any overload at the N/w traffic.Is there any way? can i use XML or database is the correct choice? If i should go with XML then how can we save it's data in to database because we need to send daily status report to customer?