Was it a nice, clear, bright pink, or was it lilacy in parts? I'm just trying to establish whether what you bought was a pink variety in disguise or wrongly labelled...

Assuming it actually was a blue one (if you saw it in flower when you bought it), seems your soil is alkaline, which is why you're getting pink flowers. You'll need to apply either aluminium sulphate (harsh on plants and roots, best not used on plants less than 2 years old) or try Sequestrene iron tonic. Otherwise, in a pot, in ericaceous compost.

Many thanks for swift response. I'll try the iron tonic I think, because it was in a pot originally.