It’s not really clear to me what your threat model is or what you are trying to protect against.
Your question asks about a messaging service, and while using a secure messenger is a great idea, it seems likely solve your first problem (“our channel got deleted by the government of UK Canada and some others”). It may be related to your second problem (your friend getting arrested) but it is also may be unrelated to their choice of messenger.
Can you clarify:
- What your threat model is
- Whether you have evidence or reason to believe that Matrix/Element had anything to do with your friends arrest (and if your friends arrest is related or unrelated to your channel being taken down)
- What you mean when you say “Our channel”, and how it getting taken down relates to your choice of messaging service?
Answering these questions should help others give more meaningful and relevant advice, and possibly give a better understanding of what went wrong that led to this point. I think the messengers you are currently using and the recommendations you’ve been given are all good choices, which of them is best for you will depend on your threat model and priorities.