isn't this a double negative sentence if nada means "nothing". So he does not buy you nothing?
I'm not so sure about that. 'In context of an argument 'He does not buy you nothing' could be refuting a claim that 'he buys me nothing.'
It is not bad Spanish grammar to use two negative in order to add emphasis. The question could equally be translated as "He buys you nothing?" What is important to remember is that "anything" can be substituted for "nothing" in a translation like this, which must of necessity be colloquial and thus doesn't have exactly the same syntax.
The end of the sentences are being cut off at the last syllable. It varies from question to question but seems worse with the male speaker. I started noticing this change yesterday.
I've had the the same problem with the male speaker since he was introduced. I often have to play his recording several time to, finally, arrive at the end of the sentence. It's interesting, though to try to guess where he's going.
I translated this to be "he isn't buying you anything". Is that not the same thing?
"He is not buying you anything" was accepted 8/6/2018. You should report this.
"He does not buy you anything" is of course a correct translation. If you're sure you have no other errors, you might want to use the report flag. By getting it added to the database, you'll be helping us all.