'Billing Arrangement' as a result of single (Paypal) purchase (beware).

I made a purchase of a Chromecast Audio device using Paypal a while back. While checking my paypal account today I realised that this purchase automatically had set up a 'billing arrangement', in effect a direct debit via my card which I was unaware off. In theory it appears the merchant could continue to take money from your bank account or credit card this way. Company concerned is MyMemory Ltd - Memory Cards, Micro SD Cards, USB Memory Sticks, SD Cards, SDHC - Free Delivery | MyMemory