‘+’ button increments quantity by 2 instead of 1

I am having an issue with the ‘+’ button incrementing the quantity by 2 instead of 1. I have added the following code to the functions.php file yet the issue remains.

add_action( ‘wp_enqueue_scripts’, ‘wcqib_enqueue_polyfill’ );
function wcqib_enqueue_polyfill() {
wp_enqueue_script( ‘wcqib-number-polyfill’ );
}

I have also added the following line of code to the plugin file woocommerce-quantity-increment/woocommerce-quantity-increment.php

add_action( ‘plugins_loaded’, array( ‘WooCommerce_Quantity_Increment’, ‘get_instance’ ), 1);

Without this code, the quantity buttons do not appear. Are there errors in the code or am i missing something?

Thanks,
Ellis