If you have an old ISA accounts still open from previous years, either stocks and shares, peer to peer or cash ISA accounts, but have not paid into since the start of the new tax year you can choose to:

Leave them open and open an new one with a different provider (the interest you earn may be lower than when you first opened the account, especially in the case of cash ISAs)
Open a new account and arrange for the old ISA balance to be transferred to the new account
Begin paying into again (if your provider allows this)

Transfers made from old ISA accounts do not count towards your annual ISA allowance so are a good way to consolidate your ISA accounts if you want all of your investments in one place.