Hi @Manaswini,
welcome to our community
You can only terminate a contract prematurely for good cause if you have chosen a contract with a 24-month term. Otherwise you are bound to the 24 months and can cancel with a notice period of 3 months to the end of the contract. You can submit the cancellation at any time, either in writing by mail or fax, or alternatively you can mark the cancellation online and then confirm it using the phone number displayed when marking the cancellation.
The note on your screenshot indicates that there is an open invoice for your contract. If you are using the direct debit system, there may have been a chargeback. Please check if you can find a chargeback on your account statement.
Kind regards
Larissa