Provider independent IP without AS and BGP - any options?

Question

Network administration

Good afternoon! The office has two Internet connections through two ISPs. It is required to ensure the acceptance of incoming connections from subcontractors in case of failure of any of the providers. According to the conditions set by the subcontractors, we need to give them one IP address to accept connections (dynamic DNS is not suitable, they need exactly one static IP address). Are there commercial services that allow us to route all traffic coming to us through some kind of tunnel to our leased addresses to ensure independence from our particular ISP?
upd: The organization of a vpn tunnel between the hoster and us and tunneling traffic from the hoster to us is the first thing that comes to mind. The problem is that it is this address that is reported to subcontractors that should be on the interface of the black box installed with us. That is, forwarding connections to us through DNAT is not good.

Answer 1

Rent a virtual VPS/VDS server from a hosting provider, set up one of the systems there that supports the VPN server function and connect to it via VPN from your office. The server accepts incoming connections from subcontractors and sends them to your office via VPN.
Server stability and static IP are provided by the hoster.
Make a VPN connection using any of the working Internet channels.

Answer 2

There are no such. Let them learn to use two IPs

Answer 3

Personal IP without AS and BGP - nothing, just a filer, it may be a way out for you to register a domain, set a minimum caching time, hang both IPs on it and remove one when falling off, even with a script, even with your hands, or hang one and change, so everyone can will give one name, if both channels work, you will also get load distribution.