Supersonic cancellation issues

I have used supersonic for a few months and decided to move to a different ISP, For cancellation they require a letter emailed or faxed to them stating the intention to cancel with a 1 calendar month period. I sent them the letter on 17 Feb 2020 and then also confirmed with them that the letter was received via whatsapp that same day. At the end of Feb I was called by a representative confirming the cancellation. He told me that the service will be stopped in the 17th of march and that my march invoice will only be for the 17 days not the full month, a few days later I received my march invoice and it was for the full month. At that stage I figured that this is probably because they require a calendar month for cancellation so I left it at that. Then around the 20th march the service stopped working even though I still payed the full amount for march. On 24 march they then sent me another invoice for April again for the full amount even though the service is not working anymore. Tried to contact them via whatsapp and phone but get no response from them. On 1 April they deducted the full amount for April from my account. This is still an ongoing battle and there is no resolution to this issue at this time.