Keep the actual submitted material, official requests, payment records and correspondence identifying the stage reached.
Make the request specific to the real file
Label amounts only budgeted or scheduled differently from completed payments. A clear record allows the actual process and financial terms to be assessed without assuming that every preliminary plan became an official submission. Identify who actually has the authority to request that a case stop moving forward: the applicant, a sponsoring employer, and an authorized representative do not necessarily have the same standing to make that request, and confirming this in advance avoids a request being made by someone the official process does not recognize as entitled to make it.
Put the request itself in writing, addressed through the official contact route, rather than raising it verbally or through an intermediary who may not pass it along accurately. Note the exact date the stop request was made and the date any confirmation was received back, since a gap between the two can itself become a question later. Keep a copy of that written request and any acknowledgment received in response, since the case can otherwise remain formally open even after everyone involved believes it has ended.
Where more than one person could plausibly speak for the case, agree beforehand on a single point of contact so the official process receives one clear instruction rather than conflicting messages from different people.