Disk Quota Exceeded error normally caused due to huge number of files in a cPanel account, almost more than 30000 files.
Generally web hosting providers put INODE limits in order to keep their servers stable as well as fast, and here in this case you got this account for FREE, so nothing to complain about.
You can do few things to decrease this INODE limit, such as delete unnecessary files like temp file, error log, any application you installed in past but not using now etc…
In this way you can avoid reaching the Disk Quota Exceeded error.