Massive overcharge for a 16 day switchover period

[#1]

I received a final bill from Plusnet for a payment of £41.74 between the 6th and 21st June. My bills prior were £24.05 which Plusnet upped to £26.80 without my consent. Because of the terrible internet connection and the fact I can barely use my phone or Xbox on it, my partner and I decided we didn't want to be with plustnet anymore which was when we received the absolutely ridiculous bill above.
Now I have covid, I am not up for trying to deal with this right now however I am being hassled, and even though I have emailed a complaint to the only listed email address in the complaint section (that specifies it is for complaints) all I have received back is an email advising it's only for mobiles. I attempted another email which was ignored. I have also sent another email through today although I don't expect a response yet.
I will not pay over £40 for 16days of broadband, especially that I can not connect to.
Has anyone else had this issue? How was it resolved?, Bearing in mind I haven't been able to talk properly for 7 days thanks to covid and I really don't want to be messing around like this but don't have much of a choice, I feel like Plusnet are trying to rip up off for as much as they can for not sticking with them and their awful services

[#2]

Good afternoon @loulou666xx, thanks a lot for getting in touch and I'm really sorry to hear what's gone on here. I know it's quite shocking to see such a high bill when you've already informed us that you're leaving. 

I don't want to go into specifics regarding billing on your account in the public domain though, so I've just tried to call you instead but couldn't get through. 

I've sent an email across explaining what's gone on here, including the recent price rise, and why your latest bill appears to be quite high. 

Please get back to me once you've had a look as we've raised a complaint on your account which I'll be looking to discuss with you. Let me know if you have any further questions too. 

You'll also find my email through your online Member Centre here.