I'm in the UK. In order to top up a pay-as-you-go SIM card, I had to first ring the mobile network to associate my bank card with the SIM before asking them to credit £10 to it (future top-ups don't require a phone call). The mobile network's technician instructed me to input my debit card's full card number using my phone's keypad, followed by the CVV. This felt intuitively insecure to me at the time, but I had no way of knowing for sure.
Is this a secure or even common practice, and does it put me at risk of having my credit card details stolen?