Went on a payment arrangement, T-Mobile contract extended and discount

[tu pac s]

permanently removed even after full pay? I have 2 lines with T-Mobile and renewed my contract with them for another 18months opting for a reduction in my monthly line rental from £35/month to £17/month. Consequently I didn't get a new phone. About 6 months into the contract I had payment difficulties because of family bereavement. Brother & father passed away within 6wks of each other. I explained this to T-Mobile and was put on a payment arrangement. After sometime both lines were suspended, can't make or recieve calls. Managed to pay in full. T-mobile now telling me line rental now £35/month and discount cancelled. Contract also extended to 24months! I feel soo awful especially considering I didn't take a new phone. Any idea how I can challenge this. I've been advised that it's company policy u lose your discounts once u go on a payment arrangement. I've been on the phone severally to them but it just seems everyone is against me to punish me 'cos I really can't get my head to understand this 'policy'