Termination troubles

I terminated their services as I was moving and it seems that informing them on the 1st of July to terminate on 31 July is not considered as a months notice. Even notified them when they confirmed the termination with the incorrect date. They are still trying to squeeze another month. A lot of correspondence has gone back and forward and they refuse to acknowledge that there is a full month between the 1st and the 31st. They must be hard up for cash. They certainly don't think about future recommendations and engagements.