it's something that came to mind, so I called to make sure.
It's something that came to mind, so I called the correct phone number to make sure. Just as I suspected, I had received a phishing email that wanted to scam me.
ご質問ありがとうございます。
「思い当たる内容だったので、電話して確かめた」はそのまま英語で「it's something that came to mind, so I called to make sure.」と言います。
また、「思い当たる内容だったのと、○○の電話番号が正しかったので電話して確かめたところ、詐欺メールだとカード会社がが教えてくれました。」と説明したいなら、「It's something that came to mind, so I called the correct phone number to make sure. Just as I suspected, I had received a phishing email that wanted to scam me.」という風に言えます。
ご参考になれば幸いです。