In Which of the Following Cases Is B Not Estopped

In which of the following cases is B not estopped from going back on the promise?

A) Alan is sent a bank statement by British Bank informing him that his yearly interest plus loyalty bonus amounts to £2,500 this year. This is higher than usual and Alan calls the bank to make sure it has not made a mistake. British Bank replies 'We don't make mistakes' and Alan decides to use the money for a trip to Majorca. Two months later, British Bank calls Alan to inform him that it had in fact made a mistake.
B) At the beginning of her lease, Alice asks her landlord Ben to clarify the provision that all repairs to the apartment will be divided equally. Alice inquires whether the outside of the building falls within that provision and the parties decide that it does not. After substantial renovation to the façade of the building, Alice is presented with a bill and a copy of the lease.
C) Amy owes Bayside Motors £2,000 for a car she purchased there several months ago. Rather than repossessing the car, Bayside offers Amy an additional two months to pay off the debt. Two days later, Bayside sees that Amy has put the car up for sale.