The correct answer is: B. He told me that he had often told me not to play with fire.
The sentence “He said to me, ‘I have often told you not to play with fire'” is in the past tense. This means that the speaker is talking about something that happened in the past. In this case, the speaker is telling the listener that he has told them not to play with fire on multiple occasions.
Option A is incorrect because it uses the present tense. The speaker is not saying that he is currently telling the listener not to play with fire, he is saying that he has told them not to play with fire in the past.
Option C is incorrect because it uses the present perfect tense. The speaker is not saying that he has often told the listener not to play with fire, he is saying that he told them not to play with fire on multiple occasions in the past.
Option D is incorrect because it uses the simple present tense. The speaker is not saying that he often tells the listener not to play with fire, he is saying that he told them not to play with fire on multiple occasions in the past.