I was wondering if you can assist me with some information......

I was recently interviewed by a Finance Director and HR Director for a Procurement Manager role. The interview went great and I furnished them with all my knowledge on how I would set systems up and make significant improvements to their company. After the interview they said I was very comprehensive in my approach.

I found out this week that I was unsuccessful but complimented on the fact that I had a good interview. the feedback was that they were looking at a different approach. I found out this morning on the job boards that they have advertised a role as a Category Buyer with have the salary. This looks to me that they have taken all my knowledge and going to use it......maybe they didn't have a role and used it to get valuable information and ideas from others.....

This to me is deceitful and unethical, is there anything I can do as the next interview I may be more cautious but by being cautious may not get me the job ?