The way you phrase your question seems to indicate that you think it's a bad apple at a merchant who is stealing your credit card, namely by using a manual method of writing down card details. Let me tell you, that that is extremely unlikely. All of your card's basic information (name, account number, etc.) is embedded within chip data, as well as in the mag-stripe. I can tell with you very near certainty that your old credit card information was stolen electronically, probably through a merchant with a compromised system.
There is literally nothing you can do to protect against electronic theft (when you use it as a card-present transaction) other than use more modernized encrypted transactions (e.g. chip), or tokenized transactions (Apple Pay, Samsung Pay, Google Wallet). If you're really paranoid about it (you don't really need to be), you can just use cash if the store doesn't accept EMV chip or tokenized.
Additionally, like others have stated, physically defacing your card is not only flatly ineffective against protecting you from 99% of modern card information theft (i.e. electronic theft), but it's also a huge red-flag for anyone that would physically handle it. They are instead likely to suspect that it is you who is a fraudster, trying to pass a counterfeit card off as a real on, as in this over-simplified scenario:
You: "Oh, you can just disregard the name on the card... it just wore off."
Them: "Uhuh... That doesn't happen. Give me a fully legible card, and a matching ID, or your sale is denied."