Interest rate changes?

Hi, i am confused, if a rise of 0.25% from 6.75% to 7.0% adds an additional £13 to monthly repayment, then what is the actual amount i am paying interest on over 12 months, can you give the calculations with answer perhaps i should mention this is not a loan repayment, but some "incidental" charges to my morgage (which is less than £10,000.00)
Answer
If 0.25% hike in interest requires £13 pm extra, this means 13x12 = 156 pa. therefore the annual interest for 7% is 156 / 0.25 x 7 = £4368