Read the agreement before you do anything else, specifically for a price variation clause. Plenty of wholesale agreements let them adjust with notice, in which case the term you thought you had is a delivery commitment rather than a price lock. If there is no such clause, an 18% jump mid-term is something you can push back on, and pushing back does work more often than people expect: usually not to zero, but to a smaller increase, a phased one, or the old price honoured on your top two lines.
When I have done this the thing that worked was being specific: your volume, how long you have bought from them, and a number you can live with. "This is difficult for us" gets nothing. "We buy 340 units a month, we have been with you four years, we can absorb 8% now and the rest in March" gets a phone call.