We use shouldn't
After Should
Expresses that a situation is likely in the future (prediction)
Expresses that a situation is likely in the present
Should is a modal verb
Expresses an obligation that is not as strong as Must.
to give advice, a recommendation or a suggestion
- They should win the game because they are a much better team. - I posted the cheque yesterday so it should arrive this week. - It should be fine tomorrow.
Sometimes Should is used instead of Must to make rules, orders or instructions sound more polite. This may appear more frequently on formal notices or on information sheets. -On hearing the fire alarm, hotel guests should leave their room immediately. -Passengers should check in at least 2 hours before departure time. -You should never lie to your doctor.
to advise not to do something, usually because it is bad or wrong to do. -We shouldn't leave without saying goodbye. -He shouldn't play with those wires if he doesn't know what he is doing.
you use the base form of the infinitive (= verb without To e.g. Go instead of To Go)
-Mary should be at home by now. Give her a call. -He should have the letter by now. I sent it a couple of weeks ago.