The first few examples I can think of are...
- You're not actually saying anything.
- You're just repeating yourself now.
- You're just going round and round.
- Now you're begging the question. / That's begging the question.
- We've already heard this.
- You've been over this a number of times already.
- You keep making this point. / You keep coming back to this point.
Also, if you are having a friendly argument or debate it sounds more polite to say "We're..." instead of "You're...", for example "Now I think we're begging the question." instead of "You're begging the question.".
I'm sure there are hundreds of other similar phrases possible, particularly if you include words like 'perhaps', 'possibly', 'might' etc. to make yourself sound more polite and respectful. :)