Lake Eland False Advertising on Facebook

I have seen on their facebook page that they advertise a 2 bed chalet for R500 per night from May to August (calling it their Winter Special.) I wanted to book from the 12 to the 16th of July. But now they want to charge me R1000 a night. So I took a picture and forwarded it to them via messenger on facebook as well as to their email address asking that the Manager have a look. By right I feel they should give it to me at R500 a night, because this is how they advertised it. Please advice how I can take it further. Maybe to a onbudsman?