Threatening letters for breach of contract

During October 2014 my wife (D Burger) received a letter from Foschini informinhg her that we are in arrears with her account no ***4***. This happened during the postal strike when there was no postal delivery. We did, however, continued to pay Foschini on the basis of a monthly average. In December 2014 we received a letter from Foschini warning my wife that she may lose her account. During January 2015 I phoned Foschini's Client Services and spoke to Eleanor Hilario, who was very helpful. They acknowledged my monthly payments which were of course then below what was required. I agreed to pay what we owed, but excluding the penalties in relation to interest, cost of correspondence, etc for the communication on the arrears. My argument is that we cannot be punished for the non-delivery of our post (monthly statements). For the last 3 months (March, April & May) I have paid R600 pm, but wish to hold back further payment unitil I am assured - in writing - that the penalties have been removed. They claim that they informed us about the monthly account via sms, but when I asked them for the cell number, the number is COMPLETELY different to both our cell numbers.