There are a number of places where FusionPBX/FreeSWITCH stores data that will continue to grow until it fills the available storage. You will need to periodically check on these and clear old data if necessary to keep your storage use in check.
XML CDR data is stored by default in /usr/local/freeswitch/log/xml_cdr/archive and inside that by year, month and day Call recordings are stored by default in /usr/local/freeswitch/recordings/archive and inside that by year, month and day CDR CSV data is stored by default in /usr/local/freeswitch/log/cdr-csv FreeSWITCH logs are stored in /usr/local/freeswitch/logs (the current one is freeswitch.log and old ones have the log rotation date appended to the name)
On Linux/Unix, to see how much space is being used you can use the du command if it is installed eg.
du -hs /usr/local/freeswitch/log/xml_cdr/archive - this will show a single line summary (the 's' option) of the usage of that entire structure in human (the 'h' option) readable form
du -h /usr/local/freeswitch/log/xml_cdr/archive - this will show the usage of each level of the directory structure below that directory in human readable form
If you need space back you can freely delete the old data.