ccj with charging order from 2005- how to settle

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lombard issued me with ccj in 2005 for 15K and were granted a final charging order, they refused to go in with a dmp with stepchange. The dmp was completed 10 yrs ago. The debt has moved several times, Idem held it the longest. Now with HOIST via Robinson Way. The agreement with lombards solictor at court was no interest to be charged if I didn't dispute the order- the debt was offer was 15.00 a mth. I had been this amount until 2016, Idem wanted more money per month so we agreed 101.00 a mth. All fine with Hoist until last month during a review with someone on mission decided I had 320.00 to spare and thats what they wanted. Mentioned in the conversation was if I came up with 4,000.00 we might be able to settle the account. After speaking to my mum and son they said they would lend me some money. Email sent- no acknowledge so I rang them, refused offer said they wanted what was was on the letter they sent me as settlement 5242.00. Back to my son he said he will lend me the rest. This where it gets odd, when I asked over sorting this out, they say we have to speak to legal dept as the balance is 5600.00 and it has a charging order- they have not got back to me. However the settlement offer and options have changed on their website. Questions I have are how does settling the ccj effect the charge ?, can interest be applied without my knowledge, if so when is this due? Is the interest charged at a simple or compound rate?Next months ddm will bring the balance to what I can get hold of. I have a letter from Robinson Way stating the account did not have a ccj from 2017 as they were asking for increased payments at the time, which I still have including all the paperwork from the last 17 years. Nearly 60 now and to be honest just want this out my life, the mortgage is finished soon. tbh I wanted to reduce my outgoings as the job situation may turn sour soon. I will only get one go at this and would appreciate any advice or a good solicitor to speak to.