mum hasn't been paying council tax, got a magistrates liability order (England)

this is long and complicated so I'll try to be concise. I'm 24, my brother is 21. I finished uni recently and moved back home, me and my brother both work full time. just before I moved back home, my mum broke up with her partner of many years who was abusive, they were both very bad financially. she's repeatedly owing money and not paying bills, me and my brother send her £400 min a month between us. my mum is SO bad with money, overspending and not paying bills on time. we get a lot of letters she ignores and I didn't want to look out of respect for her privacy but we got a scary one today. it's from Rundles, and it's about a magistrates liability order. we also got one previously (found it in the pile as I decided to open all the letters today) with a notice of reinforcement.

so that's the context, it's all under my mums name and really I just need some advice. as I said I've been at uni so this is scary and new to me. we owe over £2000 which I don't think we have between us. is my best option to try and call Rundles tomorrow to sort out a payment plan? my mum chronically puts things off, she ignores problems and hope they magically go away. we could definitely do a payment plan between us, me and my brother are happy to help pay. I just need some reassurance and friendly advice I guess. I would call today but its too late (I think). I am going to speak to my mum as well as shes currently at work and probably doesn't even know about this as she's not been looking at any letters.

I know she owes money to other places too, any general advice or resources for things like this, for herself or me, I would really appreciate. I know this isn't very concise, so I hope people understand. thank you!