The answer is "They don't never have chocolate".
Step-by-step explanation:
Even though some variants such as African American English admit the use of a double negative, in standard English, it is ungrammatical the use of this type of construction. In this case, "don't" and "never" have a negative meaning.
There are two possible correct versions of the given sentence:
- They don't ever have chocolate.
- They do never have chocolate.