problem with SIM card

Dear O2 company,

Hello. I had bought 5GB SIM card from your company about 7 days ago which can be used for 28 days. But unfortunately, I never was able to use my 5GB data service that I had paid for. Instead, there was extra payment that I never asked or was told before; 99 cent per 30MB.

Since I could not gain the service that I had paid for, I would like to get a refund. I had called the service center, but they just hung up saying that they cannot speak English. All the alternative method is closed, so I am sending this message via SNS.

Please reply ASAP,
with any possible solution.