Why did those places reject it? Mastercard should be accepted nearly everywhere, except for Lidl and Aldi.
They shouldn't have rejected it because it's not a chip and pin card - many cards aren't chip and pin, especially those coming from foreign countries, so the shops should be allowing for that. Instead of putting your card in the chip and pin device, you should hand it to the sales assistant, they should swipe it, give the card back to you and ask you to sign a receipt.