Took my car that is still under warranty for service as advised by them to bring it when it is on 30 000 km after our first service of 15 000km and they refused to service it their reason being it was due in February

Took my car that is still under warranty for service as advised by them to bring it when it is on 30 000 km after our first service of 15 000km and they refused to service it their reason being it was due in February. They wanted to push the cash payment method whereas my car is still under warranty