I'm afraid that if the calls are a result of a dialer installed on your system, then you will have to pay. There are many programs that can help stop you getting these and remove them if you do. such as click here click here and click here also click here
You can also have BT block all outgoing 090 calls.
If you search this forum there are many threads on this subject. But the responsibilty of preventing them is yours, not BT's.