We've had a couple of reports of csv files downloading as html files in the Safari Browser - and when you open them it is a jumble of letters and numbers.
This is because Safari is sometimes adding .csv.html after the file name. If you delete .html from the file name and re-open the file you will have a spreadsheet.
We believe this relates to older versions of Safari. Because it is a Safari issue we can't fix it ourselves, but if you update Safari you should have no further problems.
Alternatively try a different browser such as Google Chrome, Firefox, Edge etc.
Opening the csv file with google sheets
After downloading the csv file open a new google sheet and select 'file', 'import' then 'upload'. Choose 'select a file from your device' and look in your downloads file. Select the file you want then click 'open' then 'import data'.