Bags of rubbish

As seed sowing gets underway I need to buy bags of compost. Most composts that are available are, sensibly, low-peat or peat-free and they contain variable amounts of recycled material of various kinds. In the last I have used Westland multipurpose ‘with added John Innes’ because I have found it the better of the options. However, I have had problems with some Westland composts in the past.
But even so, I was disgusted to discover the contents of the latest bags. I tipped out a bag onto the potting bench and was breaking it up and discovered large, heavy lumps. I can cope with some large lumps of organic matter but when I managed to break these up they were large lumps of pure clay.

Compost is not cheap, costing 9 euro a bag, though usually on sale at three for two. This is not what I want to find in my compost, and quite how Westland think this is suitable for seed sowing is beyond me. And this was not one lump, but there were several in the half bag I tipped out.
What are your experiences with compost? Am I alone?
We do not purchase compost, but ours is of marginal quality. It is adequate for our purposes, but does contain many viable weed seeds. Also, it contains a few bits of plastic trash.
Disappointing and annoying.
I haven’t bought compost in ages, but that would frustrate me. I have some lumps in my compost that I “make” but it’s mostly deteriorated. How sad.
Yea, finally I was able to. Get into Comments! The last compost I bought was also Westland, though not seed compost. I got many sizeable lumps of wood which I wasn’t thrilled about!
congratulations! on getting through – not the awful compost.