To stop the time/fine running, gilly you need to apply to the Pensions Regulator for a Review within 28 days of the date of the Notice you have received. Not sure what you have received, but doubtless there is a heading on the paper which will make that clear.
Interestingly, and predictably, there is a notice on their site saying that there is a delay of 6 weeks for such reviews to be processed. Well, that will be 6 weeks in which you won't be expected to pay anything or anything further.
After they have completed their review, you can then appeal the decision, if necessary, to a Tribunal.
One of the reasons which will be considered in their review as a possible "excuse" for non-payment would be long term illness or bereavement - or maybe it was life-threatening - sorry I am not quoting this, just trying to remember what I read. Yes, that involving yourself or a key member of staff. The person you spoke to on the phone will be most unlikely to be involved in your problems or your review and will not remember what you said on the telephone recently, in your distress, so don't worry you will be able to phrase your reasons much better and with greater clarity than speaking to a person on the end of a 'phone who is only capable of ticking a box, or not. Certainly she won't be able to make any decisions concerning whether you should be paying a fine or not. As long as you contact them with the details needed to start a review, you will be able to relax a little knowing that the amount isn't accruing on a daily basis!