Commissary limits in federal and contract facilities are not just about what you can buy in a single week. The numbers in parentheses on the commissary list indicate how many of each item an inmate may possess at any given time, not just how many they can purchase per order. An inmate can buy ten tuna packets one week and ten more the following week, but if the possession limit is five, having fifteen in their locker is a violation regardless of when they were purchased.
Here is the bigger picture that explains why this triggers a SHU placement and an investigation. In prison, commissary items function as currency. Tuna, mackerel, soups, and similar goods are used to pay for services, settle debts, and facilitate informal economies inside the facility. When an inmate is found with significantly more commissary than their receipts justify, it signals to staff that they may be operating a store, involved in gambling, or receiving goods from other inmates as payment for something. A tip from another inmate, possibly someone who owed a debt, is one of the most common ways these situations get flagged and a shakedown gets targeted.
If the receipts show he purchased within limits but his locker had more than the possession maximum, the investigation is about what the excess represents, not just the count itself. Writing to the BOP and DOJ is unlikely to produce a useful response for a situation that is going to be resolved through the facility's own disciplinary process. The more productive focus is on the hearing itself and on his documented receipts showing what he actually purchased.