You can't have a static (fixed, dedicated - it's called static) IP address if you're using a public WiFi connection - the IP address is the public WiFi's address.
If the VPN can give you one of their IP addresses as your static address, you'd have to be able to forward that through the VPN app - and I don't know of any VPN app for Android that can do that. One of the purposes of using a VPN is so that no one can get to your phone. If you set it up with a static IP, anyone connecting to that IP address gets to your phone, defeating the whole purpose of using a VPN.
If you want to run a website, I suggest that you buy hosting from a normal hosting company. (Or if you're looking to transfer files with someone and you need the IP address for that, any app you run that does file transfer tells you your current IP address [that's an internal address, not an eternal address, since you're on a router], and the person can connect to that IP address. But that opens your phone up to anyone who overhears you tell them the address.)
You're trying to do two opposing things here. Maybe you should
register an account here so you can keep the conversation in this thread - and explain exactly what it is you're trying to do with that static IP address. That may not be what you actually need.