Bus lane penalty charge

Hi,

On 11th January i was driving to a hotel in sheffield city centre im not from the area so got lost and accidently drove in a bus lane for what must be a short period. . Today i received a fine letter which has now increased to £105 as apparantley the first letter they claimed to have sent, i did not receive !!

I'm ok to pay, but want to pay the original fine of £70. What can they do at this point, is there a phone number they can ring and explain, as the number on the letter is to automated payment line - 0114 273 5249 ?