The activity list is stored locally on the device. If you uninstalled or updated the app, the activity list may have been cleared in the process. There is currently no way to retrieve the activity list if it has been removed. If you need a list to prove you are being harassed, please contact your phone provider and they may be able to provide a history of calls and texts both to and from your device.
How do I clear my Activity list?
How do I know if I am blocking a number with Call Detector?