Turkish Airlines Additional Cost Compensation Claim Due to Flight Delay

 Turkish Airlines flight from Istanbul to London on July 24th at 1:45 PM was delayed, it was delayed by over 3 hours, causing my son to arrive in London 13 hours late for his summer school. We had arranged a transfer for him, but due to the delay, we had to book another one, costing an extra £100. I asked Turkish Airlines to cover this additional expense, but they refused, saying they only cover costs up to boarding. I'm asking you to please reconsider and pay for the extra transfer cost. Thanks for your help.