Let us answer the question partwise:
However, I never got to present it there due to excessive fees of the event.
This means that you never registered for your accepted paper. When you don't register for the paper, the conference committee consider the paper as withdrawn by the Author(s). This ultimately means that the paper is not published anywhere (neither online nor offprint)
want to cite this paper now...
NO, because the paper is not published anywhere (till now; considering this that you did nothing with paper after that conference)
...can I treat this paper as unpublished work ...
Yes. You can consider this as unpublished.
...or is there a formal way to say accepted in the conference, or any other appropriate way?
No. Even if you say, it does not make any sense to the listener; because, finally it never appeared in the conference. In no way, you can say the paper is published. But, historically, you can always say to your friends/peers that this paper was accepted in the Conference in Historical Age, 20XX (which does not make any sense at all)
...it makes any difference i am using Harvard citation format.
Citation does not have any role here; because, you can't cite the paper.
Side note, is it ok to upload it to my academia webpage and make a citation to there?
No. Never upload the paper to professional networking sites such as Academia or Researchgate. In stead, what you can do is you can submit this as a pre-print to arXiv arXiv And then you can submit to any other venues.
Suggestion: You can directly submit the paper to some conferences or journals in your field.