I am one of the first to jump all over the British Consulate when they do not give the service to British Ex-Pats that I feel they should but I have never found them wanting when it comes to answering the telephone during office hours. Did you call during the 2 hours for lunch time perhaps? Did you try calling after closing hours or during the weekend? Was the telephone number you were given an up-to-date one? I am NOT being sarcastic, just asking reasoned questions as I do not know the answers.
In my opinion it was wrong of the representative of Thomas Cook to refer you to the Consulate - being the CARRIER
HE should have known the answer. If he did
NOT know the answer, he should have checked with Puerto Plata office &/or Head Office in UK. In this way he would also have also learned the correct answer to give to the question when it arises again!!
To the best of my knowledge, NO British Tour company is allowed to carry a Dominican one way INTO the United Kingdom unless that person has specific permission beforehand for extenuating circumstances (emergency health/compassionate grounds normally) but they will SOMETIMES make an exception for a spouse if travelling with the spouse. Obviously this ban will be over-ridden IF the Dominican has obtained a British Passport &/or normally resides in the UK.
May I respectfully suggest that you send an e-mail to Thomas Cook (& the other airlines flying direct to UK) to their respective Head Offices in the UK & layout any mitigating circumstances that you consider might influence their decision in your favour?
Good luck but do not expect a successful outcome ~ Grahame