"According to the survey (the sample is representative) around 20% Russians support the war"
You won't trust me, but why do you trust the quoted resource without verification? The two countries are at war and while Russian propaganda is horrible, it doesn't mean that everything else is 100% true. Note that I'm not blaming the victim, the situation is close to black and white. I'm only asking whether you really believe that 75% people support the ongoing war and support starting war with multiple other countries?
There's one more aspect. Even if the sample is representative by sex/age/income/education level etc, some people may be scared to tell their opinion to a stranger over the phone. The government labeled those against the war as traitors and who knows what's the real intent of people asking such questions over the phone.
How do you think, if the war was so popular, would there be a need for stricter laws and calling people traitors?