Tira here, from Shopify Support.
I appreciate that you're using the Sesami app on your store. Have you tried looking at the FAQ on the Sesami app on how to integrate your booking button to your store? You can view their instructions listed on their website, here: Storefront integration. When you tried to reach out to customer service, were you reaching out to Shopify Support, or to the developer of the Sesami app? You can find their contact information listed under the "Support" section of the app's page here. When did you send out your message to customer service?
What kind of booking function are you looking for in regards to your store? Let me know and I can think of some alternatives for you!