Did you eat the chicken from the first two purchases? Did they smell before going into the oven? I’d definitely speak to the shop and also speak to Environmental Health at Lambeth - I think that is the borough that butcher is in. Hopefully ArchieCarlos will do the same.
Something doesn't quite smell right here and probably it's not the chicken.
Both the OP and TheWeekEnd specifically mention chicken thigh fillets.
TWE purchased £14 worth of chicken thigh fillets and they were thrown away "probably for the third time".
£14 equates to around 12 fillets which is a lot. Could some have been frozen after purchase and then thawed? And thawed properly before cooking?
TWE has a total of 4 posts of which 3 are on this thread.