Pro-Assange accounts are indeed being censored:

https://classconscious.org/2019/06/29/protest-at-twitter-hq-...

There is a media block (the UK can do that quite simply) on any reporting about Assange's health and conditions in Bellmarsh:

https://www.opednews.com/articles/Media-Block-on-Assange-s-T...

There is a definite campaign to torture/brainwash Assange while he is in Bellmarsh, as discovered by a UN investigator:

https://www.youtube.com/watch?v=8_94lj_bosc&t=3s