LCS recovering outstanding balance after account closure and moving homes

A company named LCS is asking me for money whereas the account has been closed and the online balance of this account is ZERO.
How come Bulb energy would mandate another company to collect money outstanding amounts they never took the pain to ask for directly, and not even in keeping with the online balance ?
Most of the so-called consumption of energy is posterior to the move we had notified…
Thanks for your help.

Best if you contact Bulb direct their contact details are on the bottom of the Help Page.