It can happen sometimes that when you are an employer, you have not actually made any wage or salary payments for a PAYE month such as the month from 6 February to 5 March 2020. In that case you must submit electronically an Employer Payment Summary as a NIL return by Thursday 19 March. This bureaucratic requirement is too easy to overlook.
If you engage a local accountant and business adviser or a payroll bureau to do your wages, then this will be taken care of. In our case we keep a diary and do a batch of payrolls at about the same time each month. Our payroll files are bright yellow like the old P30BC booklet so we do not overlook them. We colour-code all the taxes so green is VAT, red is income tax, blue is corporation tax and yellow is PAYE. The colour purple is used for forced loans to HMRC.
If you no longer want to have a payroll scheme, then you need to close it down in a formal way. You cannot just assume that you can stop sending in monthly returns.