When contact means ‘communication between people, countries, or organizations’, it is usually an uncountable noun, so
▪ it is hardly ever used in the plural
▪ it never comes after a or a number
✗ They live in an isolated place and have no contacts with the outside world.
✓ They live in an isolated place and have no contact with the outside world.
✗ You can only get a feel for the language by having a constant contact with native English speakers.
✓ You can only get a feel for the language by having constant contact with native English speakers.
Contact can also be a countable noun when it means ‘someone you know who can help you’:
She used to teach in Japan, and she has a lot of useful contacts in universities there.