It could be both, depending on the context. Does this sentence occur in a past tense story or a present tense one? If it is the first, we use 'had'. If it's the second, we use 'have'.

Technically, both are right! Have is the "better" answer, though, it makes more sense. My parents have never told me they were not my real parents. This is in present perfect tense, meaning it talks about the past, and the present. http://www.englishpage.com/verbpage/presentperfect.html My parents did not tell me in the past, and they have not told me in the present, either. My parents had never told me they were not my real parents. This is in the past perfect tense, meaning it talks about something that started and ended in the past. http://www.englishpage.com/verbpage/pastperfect.html My parents did not tell me in the past for some time. There are better ways to say this, such as "My parents never told me they were not my real parents", which is why the answer is "have" and not "had".

I would say both depending on the context. One is current tense and one past tense.

I thought that my aunt and uncle (are/were) my parents. My foster parents (have/had) never told me that they were not my parents. My mother was upset because I (don't/didn't) want to talk to her.