Aren't banks great?
I got nobbled by Tesco Credit Cards last month for £25 or so I think for non-payment.. which happened because I made a payment too early and it ended up being taken off the previous months bill rather than last months - so I had two payments in July, and none in August IYSWIM 
I had exactly the same problem with Nationwide back in the days when I had a Mortgage.
Two payments in one month do not count as a regular payment...
example....paid January payment and February payment on Feb 1st....had a letter saying I was in default for January and had paid March a month early.
And get this....beacause we always paid over the top when this was taken from the Jan payment it left £80 to pay. But the accompanying letter threatened repossesion !!!!!!

although we only had £1000 left on the mortgage.
Ensuing blowup had the person on the other end agreeing with me and saying I should never have been sent a letter like that....and she would pass my comments on to her manager.
So its not just credit card companies
