If we read the definition of "cancelar" that shows it as meaning "settle" or "pay off", we can see it says:

> Pagar o saldar **una deuda**.

Therefore, for "cancelar" to mean "pay off" there has to be a noun in the vicinity implying an amount that is **due and payable**, like *deuda, cuota, arancel, honorarios, capital, intereses, factura, renta, préstamo, crédito*. I don't think "plan" belongs to that group of nouns.

This online dictionary I found seems to be more specific and accurate than RAE's because it does not include the noun in the definition, but only as a reference: [cancelar][1]

> cancelar    can·ce·lar
    
> v. 
1 **Referido esp. a un documento o a una obligación legal**, anularlos o dejarlos sin validez: Si me traslado, cancelaré la cuenta que tengo en el banco. El contrato se cancelará automáticamente al cabo de un año.


>2 **Referido esp. a un compromiso o a algo proyectado**, dejarlos sin efecto o suspender su realización: Si se aplaza el viaje, tendré que cancelar la reserva del hotel. Se han cancelado todos los vuelos con los países en guerra.

>3 **Referido esp. a una deuda**, saldarla o terminar de pagarla: Si ahorro, el año que viene podré cancelar el préstamo.

It seems to me that "plan" belongs to the group of nouns under (2) above.

  [1]: http://clave.smdiccionarios.com/app.php