Short answer: homonym
Long answer:
Homograph=same spelling, different sound, different meaning
Homophone=different spelling, same sound, different meaning
Homonym=same spelling, same sound, different meaning
BUT nowadays, homonym is losing the strict definition of the word and is being used for homographs and homophones as well. It would still probably be best to refer to this as a homonym in this instance, since that is what it technically is.