Shopify Marketplace Connect

Was working OK,( the shopfiy makeover after they absorbed the app was a complete disaster ), but now our inventory is not syncing for days - we are now overselling 6-8 items on ebay everyday. They have been unable resolve the situation for several weeks now. We have to scramble to restock items, or refund purchases. Hours of our time wasted, and we look like amateurs who don't know how to run a business. And it is not cheap. Looking for alternatives.