I have been invoiced after cancellation...which cancels the refund due to me that Rain agreed on

Is Rain generally a nightmare to deal with or is it just me? This is beyond exhausting. I after not having connection for over a month and them delaying helping, they eventually sent a new router which also didnt help. They then advised me to cancel my contract as there was nothing they could do if the connection at my place was poor. I requested an immediate cancellation and refund. They have now invoiced me for April even though I have had no connection since February and requested a cancellation- which they acknowledged and accepted. So I will not be refunded, it seems. I am soooo tired of dealing with this company.