I speak out of my personal experience in this matter. Very often, during oral arguments, a litigant finds that his advocate is not adequately arguing in his favour or has maintained silence on some allegation or... The choices are as follows:
Suffer in silence. PLEASE DO NOT DO SO. Advocate may have taken bribe from the other party. Happens all the time in India. These illiterate crooks will sell their mothers if you pay the right amount. That is how low-level their professional standards are, primarily because they are at the lowest level in the academic hierarchy. If you have a doubt that the advocate is intentionally compromising your case, most likely you are right!
Seek permission in open Court from the Judge in a polite manner asking permission to say a few words. Do so, in a manner that is deferential to the advocate and the Court. Most likely the Judge will allow you to have your say. Keep it very brief. Take your frustration on the advocate outside the Court.
If for some reason, the Judge declines your request for oral intervention, then scribble on a piece of paper what you have to say, and make a written submission to the Court. Keep some ready with your case title neatly typed on top so you just have to hand write what you need to say. This is actually a better mode than the previous option as it remains on the record.
If the Judge still refuses to accept your submission, which 99% he will not, then do not hesitate to terminate the services of your advocate then and there and ask for representing yourself in person. Again do so in writing right there. This you do only in the extreme case if you believe that what you have to say, if not provided on the record, may ruin your case. GOOD LUCK!!!