Connection problems sonoff with ewlink

I have 5 different sonoff wifi swithes, pow and temp.
Not possible to connect to the duth compagny Ziggo modem. Not to reconnect to a netgear nighthawk modem. 5 years used without any problem. Just swith over to a other internet provider. s there a modem without connection problems? Or when i buy new sonoff swithes it shall work?? Sorry english is not my natural language.