This plugin doesn't return payment_complete()

I have installed woocommerce and woocommerce instamojo.
Everything is working fine except that woocommerce doesn’t auto complete the Downloadable orders.

I contacted woocommerce support here https://wordpress.org/support/topic/virtual-downloadable-products-auto-complete-order-not-working?replies=3#post-8516512

Woocommerc’s reply was this:
Virtual + Downloadable orders complete automatically if your gateway uses

our ->payment_complete() method

.

I don’t know about Instamojo – it’s not one we support officially as it’s 3rd party. Check it’s source or ask the author.

Does Instamojo have any solution to this problem?

https://wordpress.org/plugins/woo-instamojo/