I brought a Hornby Jinty at a Model Railway Exhibition a couple of years ago, it was fitted with a 4pin DCC decoder, like yours it less than the cost of a decoder, it ran perfectly on DC, I set up a DCC controller to read the decoder, the decoder was not recognised and I was unable to reprogram it, later I tried the decoder on a decoder tester/programmer it did not respond, I put in a replacement decoder and all worked OK.