Donna Peerless

I had a Cash ISA from the prior tax year and opened a new one this year. I accidentally paid some funds into the old one not realising this was not allowed as both are the same type (until recently I though as long as you only opened 1 of each type per year this was fine). Can you please confirm what I need to do to ensure that this doesn't become an issue at the end of the tax year? I have ensured i've not gone over my annual personal allowance overall. I don't complete self assessments.