How can I patch the Stripe Subscription

I'm writing tests for module which using Stripe for payment. And I'd like to make a mock for it to don't send queries to API. I use the next code for it, but still I have queries to API. I don't understand why? Such query appears at the Stripe log every time I'm running the test:

/v1/customers/cus_*********/subscription

There is my code:

@patch('stripe.Subscription.save')
def test_get_subscription_level(self, subscription_update):
    subscription_update.return_value = self.convert_to_stripe_object({...})
    # there is test code

What's the cause of this and how can I patch that query? Thanks for any help!