Hi @Jit, there should be no reason to contact your old supplier unless there’s a reason that you might think that they would object to the switch. You may want to cancel your old Direct Debit, but it’s best to check with your old supplier so it doesn’t disrupt final payments or refunds.
Although you’ll never pay twice for the energy you’ve used (as both suppliers share the same switch reading and any overpayments are always refunded), you could find yourself with two active monthly payments until your old supplier closes your account.
To avoid this you could cancel your old supplier’s Direct Debit. However, this could disrupt the process to collect final payments or refund credits, so it’s worth checking with your previous supplier before you go ahead.