If you've read the information on this website, you will see that there is no obligation on you to complete income and expenditure forms, although lenders and their solicitors imply that you must do as they ask.(posted 7968 days ago)I'm not sure what contact means as far as the 6/12 year rule is concerned. Again, as you will have read on this site, the 6/12 year rule is a grey area. Others might be able to give you more information on this.
I suspect that as the lender hasn't received any response from letters sent to your home, they have found (somehow) your wife's workplace and are trying to force you into replying to their letters by embarrassing your wife at work. I do know of others who have received letters to their workplace, but I don't know if any lenders agents have actually turned up personally at someone's work.
If someone should turn up, then your wife should not answer any questions, but ask them politely to leave and to refrain from contacting her at work again.
If someone should turn up at your home, again you can ask them politely and calmly to leave and to refrain from visiting your home again. If they don't, then you'll have to be firm, but try to remain calm but firm, you don't want to lose your temper and run the risk of getting yourself into bother.
As the lender has already located you at your home address, there seems little point in avoiding their letters any longer, if you do, as you've seen already, you run the risk of your wife being embarrassed at work. As I've said, there is no need to complete any income and expense forms, just look at the sample letters on this site for an idea of what to reply. The lender must substantiate their claim and prove that you owe them - those are the rules.
Good luck.