If the company employs you, the company is legally required to provide you with a payslip every time you are paid and a P45 when that period of employment ends.
It is imperative to receive your P45 when leaving a period of employment, and it is equally essential to provide it to a new employer.
If your new employer does not have your P45, your tax can not be deducted correctly. This is the most common cause of overpaying or underpaying tax in employment.
At the end of each tax year, you will also receive a P60 which includes totals from all employments in that tax year.
If your employer refuses to provide your P45, you might like to show them this HMRC guidance which clearly defines their legal responsibilities.
If they still fail to provide you with your P45, you should consider reporting them to HMRC, which you can do here.
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