i think its a matter of getting use to 24Option. i dont think the kind of experience u had were intentionally there to "make" users lose their trades.
what i do is, go the settings and select your desire assets and saved it for that login period.
so u dont have to frantically look for it whenever u switched between the trading features tabs and lose it.
And for all the assets that displayed, the selected time at the expiry window scroll box is always the nearest expiry window. So that takes cares of trading for the current window. but if u prefer to enter for the next nearest window just scroll it down for the nearest time.
As for invalid enteries due to change in pricing, thats inherent. sometimes it could be an advantage to you when the moment u decide to enter the asset went a 180 on you and that "annoying" system rejection message just could have saved you.
Fortunately my account manager doesnt call me until my withdrawal requests are made. thats when he briefly assures me of the likely timeline for me to get my withdrawals. Maybe u could drop him an email telling him u are in no capacity to deposit any more funds until you have made like $20K from 24Option. Until then, u are happy with what u have. He should leave u alone for now.
By far, my trading experience with 24Option (since Dec 2011) has been pleasant.