Example how to run command in running container

has anyone been able to run a mkdir in a running container successfully using the dotnet api?

I cant seem to see the directory being created in the container. this is the code i have tried: -

var created = await Docker.Containers.ExecCreateContainerAsync("3375e8971d875972dd0d5bb324c43270335a5266fa51946731b1d52192709f23", new ContainerExecCreateParameters()
{
AttachStdin = true,
AttachStdout = true,
Cmd = new List()
{
"mkdir",
"test"
},
Tty = true,
AttachStderr = true,

});

await Docker.Containers.StartContainerExecAsync(created.ID);

end result no folder in the container.

any ideas would be great.