Interest calculations!

Can somebody please confirn if I am correct (or not, as the case may be !)
Last month I carried a balance of £226 over on my card. I paid £100 off this month, and added £1500 to the total in new purchases (PE flights to LAX in Feb and a few other bits and bobs).
Last week I had a call off MBNA saying that there had been some suspicious activity on my card, ( a $1 charge to some pharmacy in Texas!) and they would close it, issue a new one and transfer the balance across.
I had the new card today, and this months statement also arrived. On the statement there was a £20.25 interest charge.
I've just rang MBNA enquiring about this, as to my reckoning I should have only been charged interest on the £226, not the NEW purchases as well, but according to them, as I still had a balance it was correct to charge interest on the new transactions from the day that they were made. They called it a rolling balance!!
Is this correct? I always thought that you had upto 30 or so days (depending on statement date etc) after a purchase with no interest added on new transactions, and then if you did not pay off the full balance on your next statement then you would be charged interest on the amount!
Sorry if I've gone on a bit, I've tried to make it as clear as possible. I am really annoyed after speaking to them on the phone, all I baisically had was "I've worked for the company for 12 years, and you are wrong!" I know it's not a huge amount, it's just the principle, and I'd just like to make sure if I am correct before I ring back again.
Thanks
Richard.
Last month I carried a balance of £226 over on my card. I paid £100 off this month, and added £1500 to the total in new purchases (PE flights to LAX in Feb and a few other bits and bobs).
Last week I had a call off MBNA saying that there had been some suspicious activity on my card, ( a $1 charge to some pharmacy in Texas!) and they would close it, issue a new one and transfer the balance across.
I had the new card today, and this months statement also arrived. On the statement there was a £20.25 interest charge.
I've just rang MBNA enquiring about this, as to my reckoning I should have only been charged interest on the £226, not the NEW purchases as well, but according to them, as I still had a balance it was correct to charge interest on the new transactions from the day that they were made. They called it a rolling balance!!
Is this correct? I always thought that you had upto 30 or so days (depending on statement date etc) after a purchase with no interest added on new transactions, and then if you did not pay off the full balance on your next statement then you would be charged interest on the amount!
Sorry if I've gone on a bit, I've tried to make it as clear as possible. I am really annoyed after speaking to them on the phone, all I baisically had was "I've worked for the company for 12 years, and you are wrong!" I know it's not a huge amount, it's just the principle, and I'd just like to make sure if I am correct before I ring back again.
Thanks
Richard.