In my opinion, the best approach is for your users to enter their data into a single repository where you can access it. This eliminates them sending it to you and you merging it into your database.
For example: Put your Access database on a network share visible to all of your users. (Or download and install MySQL or SQL Server Express – both free – on a shareable server). Provide an Access form for them to enter their data. If they prefer Excel, you can provide a spreadsheet instead that is designed to post their data to your database. Then use a simple Excel spreadsheet to extract the data and create your PivotTable.
If you want to use Excel to post data to a database but don’t know how, please see my blog in this site: Beyond Excel.