Company tries to strong arm you

I asked for a quote for certain services which I was happy with and paid but now suddenly get invoiced for hidden costs that have to be paid so they can continue with the registration of the quoted services and if I don't pay this hidden cost they can't/won't continue. The constant bombardment of marketing to "upsell" is also very annoying. The manager surprisingly did phone me back but refused to answer the question if they would be happy with hidden costs been thrown at them. They could not answer the question as to why they were trying to strong arm their customers and if the customers did not agree with this then refusing to continue with the paid services. Avoid this company