SEO help needed

Hi all, we hope to get some help with the on-page SEO of our directory-like website.

Our website is 4.5 years old and currently attracting 8.5k visits per month, with a domain authority that is higher than most of our competitors. We had over 1 million of pages targeting different combinations of category and suburb (including all suburbs in Australia), what we notice lately (past 6 months) the number of indexed pages has been declining significantly each month.

We believe it could be the issue with duplicated content (not 100% sure). For example, we have a page called "Maths tutor Melbourne" that shows tutors within 30km of the Melbourne CBD, but at the same time we also create pages for all surrounding suburbs such as "Maths tutor Collingwood". And we believe this could be a problem when it comes to Google as the search results are very similar for the 2 locations

for more you can check

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