@Loolaa22, you need to take a step back and calm down. There is nothing to actually be worried about. Your son has not received a fine or a penalty. All they have received is a speculative invoice from an unregulated private parking company for an alleged breach of contract by the driver.
Has your son received an actual Letter of Claim (LoC) from the incompetents at Gladstones, yet? I'm assuming he has and if so, you need to show us that letter.
Can your son or someone provide a clear readable picture of the sign with the terms and conditions that formed the contract?
What is that response you have shown us from the "Housing Officer"?
Can your son get his friend whose flat he was visiting to provide a copy of their lease? It is important to know exactly what the lease says about parking.
This will be very easily defended once the claim is issued. You must show us the N1SDT Claim Form when it arrives. Redact your son's personal details and the claim number and the MCOL password. However, you must leave ALL dates and times visible.