Renaging on Statements made per the Discovery APP

I have been monitoring prices at Dion Wired. In order to use my available Discovery Miles Discovery on its APP has 2 icons 1st one said Earn up to 10 x miles 2nd one says use Discovery miles to purchase from Dion Wired online Based on this fact I purchased from Dion Wired online and paid but realised no miles where deducted but instead my account was debited I called Discovery and was told that Dion Wired is no longer a partner on 27 November 2017. So I directed them to their App where it clearly showed Dion Wired online as a partner. They Adamantly refused to use my miles for that purchase. This is despite the fact that I have been monitoring this App and Dion wired for the last 6 months and nothing has changed Why should I be responsible for Discovery not informing clients that the App is incorrect? I based my purchase on the fact that Discovery published the information on their APP