There's no point arguing about the signs at the stage you are at. At the moment, by not submitting reps within the 28 day period, you have lost the legal right to submit. You can submit some now, and admit they are late and say why.If they decline to accept your reps there is not much you can do other than pay the amount demanded in in their letter of refusal to accept the reps.
Sorry, but there's no point in beating about the bush, if you do not submit reps asap, you'll get a Charge Certificate increasing the amount to £105. You cannot submit reps then at all.