Sorry to hear about your problem - but when rules change and you have been informed, you cannot complain about Dynadot. We all receive a lot of email messages every day, but I would carefully read notifications from registrar.
But you might still be successful in deleting at least a good number of your domains, provided you do it before the daily quota is reached. I have however no idea what the best time of the day for doing it is. Probably somebody with experience can let you know.