I understand. This happens in every day life too and I have to clarify and ask “did you say can or can’t?” When watching TV sometimes you don’t know but can figure out by the plot. Using cannot instead of can’t is a great option.
@NatRomanoffRachGreen Yes. If people do not speak clearly, we don’t know for sure and need to ask. I don’t necessarily agree that cannot is more formal, but perhaps it is considered so by some people. A conversation may go like this: “Did you say can or can’t?” “I said can’t— cannot.” They mean the same thing but cannot can clarify what was said.