Careless I know but my contract has become much larger, more data than I need and a higher monthly rate without my noticing - the beauty of Direct Debit.
I called customer service to query this but was told that I am on the cheapest contract (£17.55 + vat) available and nothing could be done until it expires in March yet O2 advertise cheaper deals such as O2 refresh.
Originally, our two phones were on different rates because my wife uses much less data than I do and even 2GB is enough for me.
The attitude of the person on customer service has left me inclined to take up an offer from BT, especially when she said my only options were to stay with the contact or pay £108 to leave early and couldn't explain why the cost and data allowance on both phones had gone up. Had she offered a lower rate I might well have signed up for another eighteen months.
Contracts go up every year by rpi https://www.o2.co.uk/prices#:~:text=This%20year's%20RPI%20was%20published,before%20you'd%20signed%20....
It's covered in the T&C's.
When you sign a contract you agree to pay for the full term, whether that be a standard contract of refresh.
You can only change by paying off what you owe, in your case, £108.00.
Once you have completed your minimum term you can choose to keep yoour phone and take a sim only contract which will reduce your costs further.
Unfortunately, no one here can know when or why your tariffs changed.
O2 would not change your tariff without informing you, but customer service will be able to look at your account to see when it changed and who instigated it.
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