Now that you are clear about a copy edit, a look at the content edit.
It is of no use polishing a paper if the content is lacking. Well-written nothing is still nothing. So before one can polish a paper, namely the copy edit, one needs to build the content.
So the starting point is the content. The idea is for the author and editor to work the content repeatedly until the thoughts are logical and words flow. Gaps in literature are often the most common content problem, or an unclear thesis, fuzzy questions, loose hypotheses, etc. Once the content has been tightened and honed, then the copy edit process applies. If you cannot manage the content by yourself and there is not enough help from the university, be prepared to pay the expensive rate of a content editor.
Anyone offering to write the paper for you is not an editor. Editors work with already written text. How else can you call the work your own if you did not write it in the first place. Be super careful of anyone who offers to write your work for you.