I am having problems with soldering sterling silver.

I have hard solder strip
and borax

solder paste (hard)

I have 2 options for torches
a sivert 2.kw torch
a 1300 pen torch.used for lighting barbeques as well)

I am trying to solder a silver collet to a pendant.

can anyone help as I can't melt the solder and the silver is going black each time so I am having to pickle them. I feel at my witts end with it and in a tearing my ...hair out kinda mood lol.

Please help

thank you