As a primary note you should realize that it is not an IRC Operator(IRCOp)'s job to manage your channel, by making your own channel you are saying to us that you are capable of managing users there and making intelligent decisions. If you ask an IRCOp for help registering, deleting, or otherwise maintaining a channel they may not help you if it doesnt concern the network. This is not negligence, they are not required to help you.
Next, if your channel is not registered with chanserv, dont bother asking for help even if you think it has been unfairly taken over.
If your channel is registered and you belive it's been unfairly taken over, check the founder "/cs info #channel". If you are still the founder, your channel has not been officially taken over, delete the offending Operator from access, ban them if needed, and choose operators more carefully later.
If you are no longer the founder, you must get the help of an operator immediately, the services log channel get a LOT of traffic, chances are the logs the oper is willing to check for you will only cover about 3 hours. If you catch an oper on a day they are feeling overly nice, they may search back farther for you. (Sidenote: Sephiroth and Syntax are probably the only two who will even be capable of checking services logs for you.)
The following is very important and may piss you off:
If the oper doesnt find a founder change they will not reverse the change. NO amount of your friends (or otherwise) claiming you were the founder previously is proof enough. Even the oper being a frequent visitor to your channel is not necessarily proof enough. Without definative proof that you were the founder very recently, it wont be reversed and even with the proof the oper has no obligation to change it back end of story.
Just because im tired of hearing frivolous reports, i'll include a pointless one.
<Person> Syntax, you there?
<Person> Someone hacked my channel #channel, help
<Syntax> How long ago?
<Person> Dunno, came back and I was banned.
<Person> *friend's name here* was there and saw it, he has the logs.
<Person> And the whole room knows i used to be the founder.
<Syntax> Did it happen within the past 2 hours or so?
<Person> Probably not, i tried talking to *other oper* a while ago but they didnt respond
<Syntax> Well without any proof i cant really validate your story.
<Person> *illogical excuses*!
If the founder of what you claim was your channel has been changed, the person had to have your nickserv password. This it the ONLY means we have to identify you as you. Therefore, if that person can identify for your nick we must assume that they are in fact you. If for any reason we cant find definate proof that you were the founder extremely recently your channel is gone. At this point you might be thinking im a cold heartless person who refuses to do the "right" thing and give you what is rightfully yours back.
WRONG. You may have failed to notice, but ANYONE can give the exact story you did and never have had any claim to the channel in question, a users word isnt proof. Would you like it if opers started joining any channel someone felt like claiming ownership to and set them as the founder to YOUR channel? Of course you wouldn't, that is why we require some definate proof, not because we are sadistic and like to see you suffer, it's just that as sadening as your story is it could easilly be fake.
As a final note, dont post on this forum if your channel has been taken over by another user, chances are the log will be long gone by the time an oper read it (if they ever do) so you will be out of luck.