No, you aren't making sense.
None of your questions make sense.
It depends what you mean. If you mean you have a visa to visit London, you would say 'I am in London on a visa'
Or if you mean a VIAcard, you can say 'I am in London with a Visa card'
'I am in London with Visa' would mean that either you work for VISA or you are sponsored by VISA (such as a professional athlete or musician) and VISA card has paid for your trip.
With A visa (ie the paperwork required to enter the country) or a visa CARD (a method of payment)?
When "VISA" is written in all-caps, this usually means you're referring to a VISA-branded credit card. You could say "I am in London and I have a VISA card" or "I'm in London with my VISA card" to be clearer.
TROLL !! STOP FEEDING IT !!
