Issue With Missing Credit Card Transaction and OTP records of Amazon Order

My mother's Amazon order of Rs 2,556 (which was done on 1st September through credit card) is not visible in her account's order history.

Yet she still got billed for that on her credit card statement.

She then also tried to place an order for the same amount to verify if the issue was specific to that transaction. But, she faced the same problem again.

Not just that, she didn't get any OTP on her phone for either of those transactions.

Even their customer care phone numbers aren't responding at all, and we're really tired after trying to contact them for so long.

We suspect that her Amazon account got hacked, and because of that she's very stressed nowadays.

What should we do?