The gist below will stop a user from signing up if they have ever had a PMPro order refunded unless their last order was success.

pmpro_user_any_order_refunded_last_success_check.php

<?php
/**
 * pmpro_user_any_order_refunded_last_success_check The gist below will stop a user from signing up if they have ever 
 * had a PMPro order refunded unless their last order was success.
 *
 * Add this code to your PMPro Customizations Plugin
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 *
 */
function pmpro_user_any_order_refunded_last_success_check( $okay ) {

	// If things aren't okay to start with, let's bail.
	if ( ! $okay ) {
		return $okay;
	}

	global $current_user, $wpdb;


	if ( ! empty( $current_user->ID ) ) {
		
		// if their last order was successful, allow them to register.
		$order = new MemberOrder();
		$order->getLastMemberOrder( $current_user->ID, 'success' );

		if ( ! empty( $order->id ) ) {
			return true;
		} else {

			// See if the user's has any order on record that was 'refunded', if so, stop checkout process.
			if ( ! empty( $current_user ) ) {
				$sqlQuery = "SELECT code FROM $wpdb->pmpro_membership_orders WHERE user_id = '" . $current_user->ID . "' AND status = 'refunded' ";

				$results = $wpdb->get_var( $sqlQuery );

				if ( ! empty( $results ) ) {
					pmpro_setMessage( 'Please contact us about your account to complete checkout.', 'pmpro_error' );
					$okay = false;
				} else {
					$okay = true;
				}
			}
		}
	}
	
	return $okay;
}
add_filter( 'pmpro_registration_checks', 'pmpro_user_any_order_refunded_last_success_check' );

This recipe is included in the blog post on "Restrict Checkout for Users with a History of Refunds" at Paid Memberships Pro here: https://www.paidmembershipspro.com/restrict-checkout-for-users-with-a-history-of-refunds/