Well, you are, of course, free to argue what you want. But what is their "contractual rebate" to you worth? What, exactly, is the "extent" of their obligation to you?

• If you don't participate in any frequent flyer program, it's worth nothing.

• If you participate in a frequent flyer program that awards points/miles based on distance it has one value. And that value depends on the program, the specific redemption for which you use your miles, whether you have to pay double for the redemption (e.g., too many QRPC redemptions) and other factors. And how do you discount the value if the redemption you want has no point redemption availability?

• If you participate in a frequent flyer program that awards points/miles based on spend, it likely has a different value, with the same unknowns are above.

• And then there's the issue that the miles/points don't belong to you, they belong to the airline, per the rules and regulations of all airlines. And they're subject to forfeiture more or less at the airline's whim. (Yes, there are published rules, but the airline can change them without notice whenever they feel like it.)

IAAL, and in my opinion, your chances of prevailing on such a claim in a legal context/forum are negligible. But that's no reason not to try!