Client using a website and not paying what are my rights?

Hello I'm new to this forum and hoping for some legal advice or tips and recommendations for legal contact in the UK.

I have a very tricky situation with a current client who I am in dispute with over non-payments (several invoices) worth 6+K. But more specifically they're using a website online that I designed and which contains original illustrations I've also created which is not paid for yet!

Below is my situation in a nutshell.

The client is especially delaying/ignoring/making excuses/stories to not pay after sufficient amount of reminders. I am aware the client is having financial issues but is not being transparent about it and not agreeing to any payment plan I suggested.

In hindsight, I realise now I was passively forced (blackmailed?) into putting their new website online because the client made it clear in messages that a list of verifications (that included website as proof) were required by their bank (US based) to release funds to pay me. Apparently client was having issues with transferring money over to the UK, to pay me and ex employees who are also still owed money with their own disputes.

When I say 'blackmailed'... because if I didn't put the website up no one gets paid and it's on me! So I did this out of faith or as a goodwill gesture to help everyone. I also gave login access to website because 3rd party SEO team needed it. But I guess now it was a tactic for the client to get hold of the site in a preempt that I would close down the site. Which is what happened after I closed the site down temporary.

Later realised it was all a lie and out of ignorance I closed down the site. But I guess client got a backup and had hosting tech support put it back online and client block me out completely from accessing it.

Also, a few months back the client was asking for my illustrations for (solicitor files?) and to trademark them. Fortunately, I ignored and didn't supplied original artworks. But my concern is its online now. Can the client trademark images from the website if they wanted to?

Client is an American citizen with (I'm assuming) US accounts and working in a small business in London using online fintech banking to make payments.

I am contracted as a supplier to working in-house and have a standard looking contract and NDA. Although now I shut out from all business access points, collaboration tools etc. Is this breach of contract?

Now I want to:

• To take legal action but rather find out first what my legal rights are...
• I was thinking to contact hosting to shutdown website because dispute with client for IP infringements none payment etc since I can't access website.

Thank you and I appreciate any constructive feedback.