Can you reach back out to the site developer that created your site for you? Sounds like they didn't finish the job properly and they should fix any issues if you paid them for a complete site build.
If there were errors in the coding as they set it up, they should stand by their work and make the necessary corrections. If they refuse to do so, and/or fail to respond to you notifying them of the errors, then I would definitely look for opportunities to leave an honest review on their work wherever it may be possible to do so.
There are a number of businesses such as TaskHusky for example, that will perform individual customization and/or corrections, likely for less than $800. I provided the TaskHusky link just as an example, its not an endorsement. There are several Shopify partners as well that you can seek out that will likely do the work you need for less.
You can post the job request to get quotes here.
Thank you for your question.
Please share your store URL, page URL and also password (if your store has one), I'll help you out to the best of my ability.