I have had 4 TURBTs but all for low-grade superficial tumors. There are a few things that concern me here. One is waiting four months before your follow-up cysto after your first TURBT. That seems way too long since your pathology came back high grade. Also the vitamin C -- are you sure you don't mean Mitomycin-C? Very different things. Yes, I would get a second opinion for sure. And if it really was just vitamin C, that's cause for concern IMHO. God bless you!
Did he not mention a treatment of intravesical BCG? That seems to be standard of care around here for higher grade TCC. It boosts the immune system in the bladder to help fight tumour recurrence.
Your doctor is not following standard of care. Get a second opinion. Per nccn guidelines you needed a repeat turbt to get muscle in specimen 4 to 6 weeks after first and maybe bcg if no muscle invasion. Sometimes a bad hgt1 can go straight to chemo then surgery to remove bladder but doesn't seem he is following standard protocol... there may be more to the story but look up the nccn guidelines for bladder cancer... it spells out the treatments