I need help with an extension,it says the infamous mem limit

I downloaded this paid extension called generate sitemaps or something that had good reviews, I dont like the default one.

Anyway when I go to tools> generate sitemap, the extension wont go through and says

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 32 bytes) in public_html/system/library/db/mysqli.php on line 25

now this problems comes up on here a lot and I've been able to solve it in the past by making memory limit higher in both WHM> PHP Configuration and PHP.ini file but it just wont work for this extension. My memory limit is 900mb

I've talked to my host and they said "sorry cant help you there, you have an unmanaged VPS"
cpanel forums told me to come here
dev told me its unrelated to extension

please help