Well over a decade ago I took out a 25year offset mortgage with my ExP. This was when offsets were a new product and there were only a couple of lenders offering them. It was all done online/ by phone, seemed v new and innovative etc.
We then needed to increase our borrowing to pay for works to the house. With the offset we could use our 'reserve', and basically borrow more money (I think up to about 30k more, though as you pay more off the sum increased).
Anyway basically as the mortgage amount went down, our linked current account went into debt (because of the increased borrowing). My Exp then ran up further huge debts on the account, which led to us splitting up. It ended up we owed about 80k on the mortgage, and were overdrawn about the same amount.
When we split, I was told to freeze the current account to stop him spending from it. I had to open a new account for my wages etc, and then had a standing order to pay the mortgage.
I work hard and am lucky to earn a good salary. By last year, I'd got the mortgage down to a few £100. So I contacted the provider, and said was it ok basically not to pay it (I remembered someone telling me it was better to have a small mortgage balance) and put the same amount into the linked current account, to reduce that? Yes, that was fine, as I owed less than 1 months repayment they wouldn't worry about it, as could see money still going in etc. So I've carried on, and now I owe about £65k only. So far, so good.
Years ago, as well as the mortgage and the current account, my Exp and I also used to have saving accounts linked to our mortgage...these and the current account are meant to reduce interest etc. I'd forgotten about this, but as I have some other savings with a different bank,thought I might find out if I could move it and link to my mortgage. So I gave them a call.
The call didn't quite go as expected. Firstly no one understood about these saving pots (they suggested I go to my branch. Problem is I've never had a designated branch and on the phone they therefore couldn't tell me which one to go to) but worse still I was told I was classed as a bad debtor, and I have 18 months to repay everything I owe 
This is because of overpaying the mortgage. I remember exp and I getting yearly letters saying effectively well done, if you carry on you will pay your mortgage off in another X years...etc.
Apparently every time we overpaid we were compulsorily reducing our term. I don't think this was ever made clear. Maybe I'm thick?
But I also don't get why I've never had any letters re the term for at least the last 5 years (the last letter they sent me on their system was in 2009!) or why when I called last year it wasn't mentioned?
Their attitude was well you know now, you should have known already, hard luck. Oh and make sure you pay up your £65k!
So is it all my fault for being stupid?