Do I need to pay the last payment

Hi
I received an e-mail offering a bettting system they said I could pay in 3 monthly instalments of £16.60 out of the winnings I would get I took up their offer but found it hard to get the results they were promising after 2 monthly payments I received another e-mail from someone else offering this system or free,so I cancelled the last payment explaining why but they said I had entered an agreement with them and must pay the last instalment or they will take it further and it will incur more costs to me.Can they do this as I signed no agreement

If you didn't sign anything they can't collect. Make sure you didn't give them access to any financial information.