********** transaction: Amazon TV contract

On 14 December 2019 I bought presents on Amazon AU for my grandchildren in Australia. On 13 January 2020 I got a message from my bank that on 12 January R577.75 had been withdrawn by Amazon, apparently for a TV contract: AMZNPRIMEAU MEMBERSHIP +*** AU. I did not order anything from Amazon and I did not get a message on my phone to OK this transaction.