Unable to connect the network (but its the account problem)

[LazzyReaper]

So basically my friend was playing on the server but then he was kicked out of the server and just unable to connect the server when ever he tried to connect it just says Network error unable to connect you to the network. At first we thought it was my friend's connection or computer problem. However when i tried to log into his account and help him do contract it also says the same and that goes for my other friend as well when they are trying to log into his account. My friend tried to connect to other server and it was completely fine. So we dont know what really happened we tried to send a ticket but nothing works out its not the banning problem or any connection issue. Therefore im wondering if its the problem with the complex server reading his account. Well if anyone please knows how to fix please help
Here are the things we tried:
turning off firewall
reinstalling complex
reinstalling technic(which we use to download the complex pixelmon pack)
trying to log in to the server using the (Vanilla)Minecraft launcher (but still shows the same)


all in all i feel like this is like the problem with the server rather than the player itself as ive said that when he use other account its completely fine and when we are using his account we also face the same probelm and my friend is already dying from not being able to play the server(he is addicted to it) so please help (so that he can stop being depressed)

 

[DinJarinM]

Id try going to cmd (just type it in windows search its command prompt) and type ipconfig /flushdns and after that try ipconfig /renew and then reboot pc and try to log in