There is no one perfect place to store information. Microsoft Office 365, Dropbox and Google Drive are safe platforms to report and save records, but only if you all know how to use and access them securely. If you are not comfortable in using computers, it may be safer to receive reports by phone call, and keep written records in a locked drawer of your house or office. The most important thing is that they are kept confidential and locked by either password or key.
The NSPCC have produced some helpful guidance about recording and storing information, which you can download here.