Arrears on old cancelled membership from over 4 yr

I had a contract with Virgin Active over 4 years ago. I lost my job, and was unemployed for a long time. Now my life is back on track and I would really like to join this gym again in Krugersdorp. They insist I pay 50% of the arrears (3months) for a time my card was cancelled, and I couldn't use any of the facilities (My card did not even give me access to the gym)? How can they expect me to pay for a service I didn't or couldn't use? I lost my job, had no income, am a single mother and had no control over what happened to me? Gyms make a lot of money, and its strange that when people want to join, they still insist on bleeding you out to get every last drop of blood. Giving me 50% discount does not justify the fact that I cant pay for a service I DID NOT USE. The person I spoke to Bianca Ross was very kind, but unfortunate cant help me. Here you have a guaranteed contract income for the next 2 years, but refuse to assist with writing off a debt (for something I COULDNT USE)