When trying to make a reservation I receive a very weird rate error, see picture hereunder

The total rate for my reservation is around $600 for 3 nights, taxes are around $100. So if I count this up I should have something around $700 in total. The booking engine displays $1,300...

When calling the reservation line I receive this same $1,300 and no explanation where the difference comes from...

The strange thing is that hotels.com gives me a rate of approx. $700...

Please enlighten me, because I'm really confused... what am I missing?