Salam ive heard that when a husband calls his wife it is obligatory to answer even though she is praying namaz is it true?
Interrupting an obligatory prayer intentionally without any valid reason is forbidden according to the consensus of Muslim scholars because it undermines worship which contradicts with its sacredness and high status.
Allah SWT Says ( meaning):
O, you who have believed, obey Allaah and obey the Messenger and do not invalidate your deeds. 47:33
The exception is when there is a life threatening situation including medical emergency.
So to answer your question, a husband has no right over Allah SWT's instructions and that is to complete your prayers without interruption.