3 ISPs with one public IP

My situation is this: I have 3 different ISPs: VIVO, TIM, and NET here in Brazil (1 Static IP and 2 Dynamic). I need to do 3 things:   1) Connect my 3 ISPs on one device.   2) I need to use only one public IP to connect to the internet. Every single workstation needs to connect through this IP as if there is only one ISP connected.   3) If the main link goes down, another link could assume its place but the same old public IP still must be used.  

Is there a way to do that? Any appliance, proxy, or DDNS?  

Thanks in advance.