HKA interview questions

Had 2 relatively informal interviews in quick succession, including meeting in person in the London office. After chasing for an update, I was called and told they were would be delighted to offer me the role and would beat the salary of another offer I had on the table. I accepted HKA's offer and was told multiple times my contract would come in the next day or 2. When I chased for my contract so I could turn down the other offer I had on the table, I was told "it's just a formality needing a contract, of course I can turn down the other offer and we'll get the contract to you tomorrow". A week later (after chasing numerous times for a contract) I was called and told in a conversation lasting less than 3 minutes that HKA were rescinding my offer for "someone internal" and was rushed off the phone with no explanation. Totally different experience to everything I had read online about employee experience at HKA and safe to say something I have never seen or heard of in almost 10 years in HR. Disappointing and incredibly unprofessional. Hopefully this is a one off experience that doesn't happen to anyone else.