secured loan advice

[chester]

We have secured loan on business premises and overdraft, the bank pulled overdraft and when we complained called in loan as well. New accounts have all been sorted and we have been trying to negotiate full and final payment but bank not interested as they have legal charge on our business. My question is can they pursue for full amount on secured loan if they have lost paperwork. I have this in writing .
We have agreed a monthly instalment payment to start this month but honestly would prefer to settle to release charge on business.
Is it worth approaching solicitor or mediator and if so can someone recommend one or give me idea on charges.
Thanks for reading