I own a BV9800 Pro which works fine. But since yesterday when I switch it on,The phone doesn't pass the step after I enter the PIN, its loop back to the begin all time. What can I do? Please help

hello,
first excuse my poor english (I'm so french !).
After 10 years with a samsung xcover3 which is still working ! I finally bought a Blackview 9800pro 9 months ago.
recharging the battery is now random : the first 6 months i usually can use my phone 3-4 days...
since 2 months, all 4-5 recharging the phone, it works only one day.
but the harder is that it boots 2-3 times a day now !!
 when i switch on the phone, i have to enter the PIN, then the diagram, then have to wait for the end of the boot... 2-3 times a day.
it's not been A year i bought this phone !!!!
thanks for reading my post...
more thanks for responding to me...