Overpaid Last Year

Hi,

- I worked for a company for 2 days in September 2017. They paid me £600.
- In April 2018 they email me saying they paid me twice, please return the money
- I check my bank account statements and to my surprise, they are right. But the money has been spent unknowingly.
- I inform them that i am recently unemployed (as of April 2018) and will struggle to return this money
- they email back with a deadline of 2 weeks
- I do not respond
- They chased me up today threatening legal action
- i inform them i have very recently started working again but given the period of unemployment I can not pay in full. I offer installments of £50 a month
- They demand £200 a month or they will take me to court
- Eventually I offer £70 a month
- They demand £100 a month or they will take legal action (they are an international media company).

Do I have any rights here? I wish I had noticed the overpayment initially. My invoicing was correct.

Urgent advice needed! 🙂 I really don't have £600 spare to give to them.