Hi there,
Sorry to hear that you haven’t had much success. If you link your listing to your forum bio, members can review your listing and give advice; this is often the best way we can help you. In the meantime, you might want to check out this blog I inspired for THS about mistakes to avoid when creating a listing - have a read and see if your listing can be improved.
About invites and calendars:
Remember that the most successful way to secure a sitter is to have a stand-out listing that attracts applicants, rather than through sending invites. Invites occasionally work out for some owners, but most owners secure sitters via applicants; these are the people that actually want to sit for you and are available for your dates!
A sitter’s calender only shows availability according to dates that they’re booked / not booked for another sit on THS. A sitter cannot input dates that they’re actually unavailable for THS. So, the calendars are rather unusable and inaccurate. This is a big reason why sending invites rarely works out.
Hope that helps! 
(And here is how to link your listing to your bio if you’re unsure):