I hope you didn't actually "withdraw" the money from last year's ISA! If so you will have lost last year's allowance and will ony be allowed to invest this year's £3600
What you should always do if you want to move it from one ISA provider to another, is to open an account with the new provider and then request them to transfer from your original provider, doing it that way means you can keep each year's allowance intact, therefore allowing you to build up a substantial tax free pot over several years.
I suggest you look at the Moneysupermarket.com best buy tables to find the best Fixed Rate for 12 months, things change continuously, so last month's best buys aren't necessarily this month's, but with a fixed rate, once you've made the deposit, the rate is guaranteed.
Good luck