Please help have been trying this for 5 weeks(Headbang)(Headbang)

J is encrypted as S and S is encrypted as N encryption map y congruen(ax+b)mod 26,decryption map x congruent(cy+d) mod 26

HKHYKXOOB NTHPKYHNYN EHE KVY YXDP YWP TVKTPGY VA IOXTD WVOPN NPCHVJNOB