A Synology NAS would be a good shout if you don’t mind the self hosting and maintenance route. That said, I also have an Infomaniak kDrive setup for my cloud backup. With that I have my email, calendar, drive space and it even offers an office suite in the cloud.
It may not have all the bells and whistles you get with Microsoft Office but, for me, it certainly does the trick.
It has already been said but the company is complying in the sense that it is providing a solution whereby you can delete your account. That said, where you are unable to follow that process, they should offer you the same ability via email. Each company does things slightly differently but I would hazard a guess that an email stating that you find it more reasonable for the action to be carried out via email, they would be likely to comply.
The reasons why companies put these in place is simply to avoid mass requests for deletion and, as stated, to also protect you.
While email spoofing has been mentioned, it is somewhat unlikely anyone would send a request for deletion after spoofing your email, yet, it is not impossible.
You may have to be persistent, could use services that support or even get some pointers from the ICO. Here is a really good link https://ico.org.uk/for-the-public/your-right-to-get-your-data-deleted/
I wish you luck