The divorce bill was part of the terms we agreed when we left... we have indeed paid in, but we had already agreed to a number of long-term spending commitments before we chose to leave, and this is to ensure that those commitments are kept.
It is not in our interests to be reneging on commitments... we need new trade agreements - and quite a lot of them - to get back to where we were as EU members... we cannot expect people to make agreements with us if we prove to be unreliable.