No problem, as I say I am no expert. I think possibly look deeper into who your market actually is and see how those people interact with social platforms and buying on the web?
Personally I can see no fault with your website so it must be SEO related and possibly that the site is not being showed to the people most likely to buy. How do you market the site? Personally before paying for anything further I would look into pay per click marketing - if you are going to pay money for experts why not look into this form of marketing and get help for free from a google accounts specialist?
It sounds like you have put an awful lot of money and time into SEO so this would be the next stage I would think and maybe look for similar directories in your main markets that you can join up to - also do you know who your competitors are? You could contact Ahrefs and see if they can help you by seeing what your competitors are doing to promote their businesses and do the same?
Lastly I follow a guy on youtube who is very good and goes through a lot of marketing strategies. His name is Elliot Prendy - his channel is really good and very inspirational - maybe take a look at some of his videos for some ideas on how to get the brand out there.
I really hope this helps - just thought I’d follow up as I know how you feel and it isn’t nice. I can really appreciate the hard work you have put into your website and feel that you can do this without paying stupid amounts for little gain - pay per click should at least break even and then you can set up funnels to recapture the lost customers with discount codes etc… its just finding out who those customers are… all the best and don’t give up! 