Redbridge guy again, I managed to talk to someone else that explained that the Employer NI is a monthly allowance, not yearly. I don't know if that's the case as this is my first Umbrella contract. In regards to Furlough I asked again and was told the same thing, they don't pay furlough so nothing I can do except claim Jobseeker Allowance or Universal Credits, but I would need to terminate my employment contract with them.
In regards to lock-down, even though they are our employers, we get absolutely no support from them. Lucky I can claim minimal furlough through my LTD company as I didn't close it down yet, but this is barely enough to get me by, around £500. Might be better off applying for unemployment.
Can't comment on the general service, I never talked to them except for setting my profile up. But never had problems with payment. Their monthly charges are £84.