Pitney Bowes - Anyone had luck cancelling their contact?

Since Amazon introduced the tracking service for all sales we have been unable to use our Pitney Bowes franking service as it does not offer tracked for large letter .

As 99.9 % of our orders all go out this way- Pitney Bowes say they will not cancel the contract unless the full service charge and hire is paid for- 3 plus years worth.

That's even though they have been sitting on a credit since March last year.

Has anyone successfully managed to cancel their contact and if How without having to pay for something one cannot use.