There has been a long history of problems with optimum online ... back in December all their p2p clients could not connect ... The problem eas a technical one and a lot of posts were made here about the subject in such a way that finding them is not exactly easy lol
So we really don't know if the problems have been fully resolved.
Please get on to them and tell them your problem , and if they say here is not and has never has been a problem, get some one who knows what they are talking about. Search above right for optimum or OOL and see what else you can find ... but please update us as to what happens when you speak to optimum.
I have no idea if Birdy's reply or mine will solve your problem ... but I'm fairly sure one of them will