Unfair behaviour towards a customer

I had a 1 year contract with Crisp fibre, from 01 May 2021 until 30 April 2022. I notified them via email on 25 February 2022 that they should deactivate my account with effective date 30 April 2022 as per my contract with them. They acknowledged my email and a link was sent to inform them online, which I completed and even stated that they should not debit me after 30 April in the comments section as my lease expires then and I needed connectivity until that date only. I then got an invoice for May on 22 April and I advised them I would not be able to pay this amount as I did send them the necessary info. Long story short, they want to charge me for May. Im not even at the specific site in May and there was a message where it was confirmed by the agent that I will only be billed until 30 April. This is unfair practice against customers. It is not my fault the online form did not go through, I did the necessary by informing them via email. They are refusing to see my side and also refusing to give me contact details of their complaints department so that I can take it further. This is really disappointing service