That's kind of an older banking code problem. I haven't had this problem in years with Bank of America, but basically if you paid with a debit card, for some reason it took their programs longer to process a return of funds to your account. (I suspect it was because uses "real" money). A credit card would net an instant change in balance...(because it's credit--the sooner you get it back the sooner you spend it again!)
In practice, many places will still give you a cash refund for a debit purchase (because of customer complaints about the time lag)... But, again, I haven't had trouble like that in over 5 years, maybe longer.
They will say it takes longer, more as a "cover your butt" sort of a thing, since it sometimes can take longer, and they don't want anyone to sue them over it. But in most cases I've noticed it goes back within about the same amount of time as it took to come out.
these things are bound to happen when technology grows leaps and bound-within a micro second the funds can be transferred to any part and when you report this fraud the bank will make necessary investigation and this process takes time
There's not really much interest that banks charge or keep money to get interest anymore, but that's what started it. By delaying your refund the bank is earning interest money on your money rather than you. You're only one person but imagine all the folks waiting on refunds while the banks collect interest on the funds. When you make a payment the banks hang on to the money for 2-3 days, earning interest on what was your money. Today it's very little interest but when the banks were making up the rules, interest rates were much higher.