Termination fee refund

Hi, I was on a one month contract with ID mobile costing £4 per month for a few months and when I found a better deal elsewhere I asked for my PAC code and sent it to the new provider. When my final bill arrived I discovered that I’d been charged a termination fee. I learnt from someone else’s question on this forum that you charge this for not having given 30 days notice! As I was on a one month contract I find this answer entirely unacceptable. I opted for a monthly plan so that this wouldn’t happen! It also feels like it’s a policy that runs against the whole reason PAC codes were introduced. I expected at the worst to pay to the end of the month in which I left but to charge me more than £50 (equivalent to more that a years worth of monthly fees) for leaving for a better rate else where  is insane. I’d like this charge deleted please. Let me know what I need to do to make that happen.