Time and time again, I was told that the issue was with my hosting account as they had not heard of anyone else with this same issue.
Today, I have received this ticket reply from my Hosting:
I have checked that the SMTP script/plugin which is installed is working fine from the wp-admin while sending a test email, email also working fine from your domain webmail.
It appears that the contact form on your website and the SMTP plugin setup are having some connection issues. Please recheck the current theme you are using for your wordpress website and make sure that there SMTP script is properly fetching to your website home page, please check the same with the help of your website developer.
So has anyone else who is using or has used the Rockstar Biz Theme, had this problem?
I don't have another hosting account to try the theme on so I don't really know where to go from here.