Whether there was notice or not, you are entitled to the refund for which you contracted and that is what you got, e.g. the fare difference.

EC 261/2004 does not apply.

If you did not receive notice of any kind and have checked with any possible source and your spam filter, complain about lack of notice, you may see some type of customer service gesture, although there is no particular compensation.

If you purchased through a TA or third-party site, it is for the TA/site to notify you.