Previously I used SoftEther VPN to connect from home with my corporate network. That's because it works through the ISP firewall & Corperate firewall & no static public IP needed. Although I found SofthEther difficult to setup.
I am searching for a guide or software to setup a VPN between the network of my clients & my own network over the internet. What can you advise / recommend?
A DynDNS service is the least you need to implement. After having a valid DNS entry pointing to the current public IP, your options are many. E.g. using OpenVPN, optionally with the HTTPS port if otherwise blocked. You would have to create certificates for server and every user or machine connecting.