Im a bit confused

You say you were using extra water, didnt know where it was going, then found a frog was causing one of the wc cisterns to not fill.
I suppose the same frog could have been sitting on the float valve and causing the cistern to overflow ?
A frog could have worked its way up the sewer pipes but I cannot imagine how it could have got into the cistern. Small boy with a new pet he didnt want anyone to know about ?
Ive come across people who have had a big water bill when WC washers fail a bit and the internal overflow allows continuous seepage into the pan. Its not obvious like the old traditional overflow pipe is. So much for WRAS approval.