I need help making a Personal Hotspot on my iPhone?

I know how to MAKE a Personal Hotspot on an iPhone

But the problem is WHEN I DO it kicks me out of my own Wi-Fi and forces me on LTE for some reason, and I have very bad LTE and I don't want to pay for better LTE.

But if anyone has a solution to why my iPhone kicks me out of my own Wi-Fi when I make a hotspot, Please tell me it would mean a lot to me!

iPhone detals:

iPhone 5c, (Updates are no longer given to 5c iPhones)

Not modified, A Regular iPhone with no modificatons, I bought it off eBay.

Very good condition, Just need to turn the phone off and on (NOT SHUTDOWN) if the phone screen starts to glitch (Which it doesn't usually do)

iOS 10.3.3 (14G60)

Well that's all I have to say.

IMessage activation problem?

My iPhone pops up with this error message when trying to activate iMessage;
"Your carrier may charge for SMS messages used to activate FaceTime and iMessage"
What does this mean?

Which off brand lightning charge cable for iPhone should I buy?

I have tried the cheaper ones on eBay and one from the tiger store but they wobble in the socket and don't charge it. Can anyone recommend a brand as I don't want to pay for the apple one.

(Also it isn't the phone that's faulty as a friends cable worked)