We haven't had a mortgage for years now, but when we did, it was on Direct Debit. We received a letter from our building society saying that a particular month hadn't been paid - shock horror!
On checking with our bank, they said our d/d payment had gone into someone else's account - not to the building society! This wasn't the first error they had made either!
Needless to say, we weren't impressed & switched banks!
Ever since I've been doing electronic/online banking, etc., I/we've had no further problems.