Subway complaint: MOULD ON MY FOOD

My sub had mould on it, I took it back and the man who served me tried to tell me it was just ‘paper towel’ . I then told him it was clearly mould in two places and he argued with me it wasn’t mould. Another man then came out and said we will make you another sub. I said I was now put off of the food and did not want another subway right now as it’s made my stomach turn. They said all we can do is make you another sub today, I said can you atleast provide me with a voucher for a free sub for another time and they said no. I then asked for the manager and they said he wasn’t there, I then said I would report and take this further as it’s bang out of order and has put me off of their food. Not only did the close to get refurbished not too long ago due to rats, their food now has mould on too. One of the men then went and phoned up the manager and came back and said I could have a free sub for another time. I asked him to take my name he wrote it down with the date, however I am not satisfied, I was given dirty looks from the man who served me the whole time the debate was going on they wasn’t helpful or trying to please the customer.