The branding and use of what constitutes a "debit" card versus a "credit" card differ per country and unfortunately, the card associations and banks have utterly confused people about what the difference is and where each can be used etc.
A pure debit card which is not branded Mastercard or VISA and which has no expiry date cannot be used as a credit card.
These cards are what are commonly issued in South Africa and are termed debit cards (normally branded Maestro).
These cards cannot be used as credit cards:
There are however other cards, also termed debit cards, which are actually credit cards under a different guise, often referred to as cheque cards. These have expiry dates and will have Visa or Mastercard branding and can be used online.
These are what are typically issued in the US and the UK etc. as debit cards: