Three different ways of saying no thanks without being too aggressive. Hopefully anyone receiving these replies would understand your point. If they still continue, there are many more less polite versions
"no thanks" （結構です）と言う、あまり攻撃的では無い3つの表現です
この返答を受け取った人が、あなたの気持ちを理解してくれるといいですね。
もし、それでも続くようだったら、もう少し丁寧ではない表現もあります。
"I am not interested in video chatting."
Interested - something I want to do. If you are answering a friend you might say, "I cannot video chat right now." OR "Let me call you later."
If it an unknown person you could also say...."I do not accept calls from strangers."(Stranger - someone you do not know) or "I am not interested in talking."
I am not interested in video chatting.
私は、ビデオチャットに興味はありません。
interested-興味がある
友人に答える場合には、下記のように言えます。
I cannot video chat right now.
ちょうど今、ビデオチャットできないんだ。
Let me call you later.
後で、電話するね。
もし、知らない人なら、下記のように言えます。
I do not accept calls from strangers.
知らない人からの電話には出れません。
Stranger -知らない人
I am not interested in talking.
話したくありません。
I'm not interested in talking to you' is a polite way to tell someone that you don't want to talk to them; this includes phone calls, video chats and written messages.
'I don't want to video chat with you' is telling someone you don't want to video chat them, this does not include phone calls and messages.
'Please stop contacting me' is, again, a very polite way to ask someone to cease contact with you. You don't want to receive any further messages or calls from this person at all.
I'm not interested in talking to you（私は、あなたと話したくありません）は、話したくないときに使う丁寧な表現です。これは、電話、ビデオチャット、文面のメッセージに使います。
I don't want to video chat with you（私は、あなたとビデオチャットをしたくありません）は、電話や、文面のメッセージは使えません。
Please stop contacting me（連絡するのを止めてください）は、あなたとコンタクトを取るのを止めてもらいたいときに言うとても丁寧な言い方です。その人から、これ以上のメッセージ、または電話を受けたくないときに使います。
If someone is becoming a pest and causing you stress, you need to tell them to stop contacting you. Such activities are becoming more and more criminalised these days and this person should be made aware of this point. Perhaps you can unfriend or block this individual? Anyway, sentence 1 would probably be the clearest. When you say, 'never, ever' in a sentence, you are stressing that something will not happen.
I am not going to chat with you so leave me alone.
No, I will not video chat with you. Stop contacting me.
Sorry, not interested. Stop contacting me.
I am not going to chat with you so leave me alone.
No, I will not video chat with you. Stop contacting me.
Sorry, not interested. Stop contacting me.
Please stop contacting me. My answer is no.
If you contact me again, I will report you.
I am not going to chat with you so leave me alone.（あなたとお話しするつもりはありません、ほっといてください）
No, I will not video chat with you. Stop contacting me.（いいえ、あなたとはビデオ通話しません、もう連絡してこないでください）
Sorry, not interested. Stop contacting me.（ごめんなさい、興味ありません。もう連絡してこないでください）
Please stop contacting me. My answer is no.（もう連絡してこないでください。私の答えはノーです）
If you contact me again, I will report you.（もう一度連絡してきたら、通報します）
You ahve to be careful when using social media as you might not know who the person is (stranger) so you might want to tell the person to leave you alone or you do not speak/video chat with people you do not know (strangers) a simple way is to tell them you are not interested
イギリス 
アメリカ合衆国 
