This is appalling behaviour on the part of the solicitor. He or she has no right to make such insinuations. My response would be to ask that solicitor why they hadn't studied harder in order to avoid being a "yellow pack solicitor" chasing people for mickey mouse debts.
It might be wise to find out what address the debt management company are using.
I find it peculiar that a bank would issue their solicitors with a wrong address instead of using the address of the debt management company they would have been corresponding with.
I've returned all letters as mentioned and refused to sign for registered post. I've also returned letters from the debtors accountant, stating clearly that they do not live at this address.