I am surprised you paid instead of contesting the bill. I wouldn't even allow someone to rip me off at all. I would flatly refuse to pay until they bill me correctly.
Right now I just use a Powerbank for my phone and mobile data, but getting a UPS for my routers so I can use my fibre internet. I eventually want a generator, but going to be a long time since I have enough money for one.
ye it's very hard to find one at that price locally I wish you luck, the battery life isn't made to be off the battery for too long with gaming machines